Wastewater Management

Wastewater is any water that requires cleaning after it is used. This includes water that has been used for laundry, bathing, dishwashing, toilets, garbage disposals, and industrial purposes. Wastewater also includes rainwater that has accumulated pollutants as it runs into oceans, lakes, and rivers. Pollutants are unwanted chemicals or materials that contaminate air, soil, and water.

The goal of wastewater management is to clean and protect water. This means that water must be clean enough so that it can be used by people for drinking and washing, and by industry for commercial purposes. It also must be clean enough to release into oceans, lakes, and rivers after it has been used.

Wastewater is usually divided into two major groups: point source wastewater and non-point source wastewater. Point source wastewater includes wastewaters that enter natural waters (such as lakes, rivers, and oceans) from defined locations. The most common point sources are sanitary sewers and storm drains.

Non-point source wastewater is wastewater that is not connected to a specific source. This includes runoff (water that drains away) from agriculture and urban (city) areas, and acidic waters from mines. In many ways, point source waste-water is much easier to manage because its source and the pollutants it contains are known. Non-point source wastewater, on the other hand, is both hard to identify and treat.

Wave Energy

The oceans store large amounts of kinetic (moving) energy from the wind. The wind generates waves as it blows across the sea’s) surface. The larger the wave, the more energy the wave contains. Wave energy provides a continuous source of renewable, non-polluting energy that can be converted to electricity at wave power plant sites around the world.

Where the waves are

Windy coastlines around large oceans are the best places to build power plants that harness wave energy. Strong winds that blow continuously over long stretches of open water create the largest waves, which contain the most energy. Strong, steady winds that blow in Earth’s major wind belts (zones of wind in a prevailing direction) generate massive waves.

In the subtropical zone on either side of the equator (imaginary circle around Earth halfway between the North and South Poles), suitable wind power sites are along east-facing coastlines in the path of the westerly trade winds, such as the east coast of Florida. (Winds are named for the direction from which they blow; the trade winds are strong winds that blow from east to west in the subtropics on either side of the equator.)


An aquarium is any water-filled tank, pool, or pond in which fish, underwater plants, or animals are kept. An aquarium can be as small as a glass bowl for a goldfish and as large as a pool for a whale or a marine museum.

History of fish keeping

The ancient Sumarians (2500 b.c.e.) were the earliest fish keepers. Fish keeping developed as a way to provide and store food. Fish were caught in rivers and then kept in small ponds until they were used. The ancient Egyptians also kept fish in ponds, but not all of their ponds served a practical purpose. Egyptian hieroglyphs (a system of writing that used symbols and pictures) and art depict fish and fishponds as decorative objects.

In ancient Iran, China, and Japan, fish keepers bred special types of fish for use in decorative ponds. Fish keepers created koi, a popular decorative fish, by selectively breeding carp (a fish used for food) in pleasing colors and sizes. The present-day common goldfish, a close relative of the koi, is also a result of these ancient breeding practices.

The popularity of fish keeping spread to Europe and the United States in the eighteenth century, when ornamental fish were imported from the East. Fish keepers maintained ponds of ornamental fish, but the fish could only be viewed from above the water’s surface.


Ecology is the study of the relationships between organisms and the relationships between organisms and their environment. Ecology was first recognized as an academic subject in 1869 when German naturalist Ernst Haeckel (1834-1919) first coined the term ecology. The word is derived from the Greek words eco, meaning "house" and logy, meaning "to study," indicating that ecology is the study of organisms in their home.

Ecologists often distinguish between two parts of environment as a whole: the living or biotic part and the nonliving or abiotic part. The biotic part of the environment includes all organisms such as animals, plants, bacteria, and fungi.

The abiotic part includes all physical features like temperature, humidity, availability of light, as well as chemical components, such as the concentrations of salts, nutrients, and gases. Ecology, then, is the study of the relationships between and among the biotic and abiotic environments.

Ecology as part of the biological sciences

The components of the biological world are often organized along a spectrum. Assuming the spectrum is laid out from left to right with the left being the smallest, atoms are at the far left. When atoms combine together they organize into molecules, which are just to the right of atoms on the spectrum.

Hydrology and Hydrogeology

Hydrologists and hydrogeologists are water scientists who study the properties of freshwater and its distribution on the continents. (Oceanographers study the physical and chemical properties of salt water in the oceans.)

Together, hydrology and hydrogeology provide information on how to manage and protect freshwater, humans most essential natural resource. Hydrology and hydrogeology are distinct fields of study that employ different methods and techniques, but they overlap to provide a complete picture of Earth’s freshwater resources.

Hydrology is a branch of engineering that deals with the physical properties of surface freshwater, such as lakes and rivers, and with its chemical interactions with other substances. Hydrogeology is a subfield of geology (study of Earth) that, by definition, specifically addresses groundwater—water moving through tiny openings in rock and soil layers beneath the land surface.

In practice, ground and surface water interact as a single system. Surface water seeps into the ground and groundwa-ter emerges to the surface. Hydrogeologists work to explain the geological effects of surface water in rivers, streams and lakes, and hydrologists lend their technical expertise to the mechanics and chemistry of moving groundwater.


Limnology is the study of the chemistry, biology, geology, and physics of waters that are found within continents. In contrast, oceanography is the study of open ocean waters. Waters found within continents may be lakes, reservoirs, rivers, or wetlands (land where water covers the surface for at least part of the year) Although most limnologists specialize in freshwaters, the study of saline lakes, like the Great Salt Lake, also falls under the discipline of limnology.

One of the more important goals of limnology is providing guidelines for water management and water pollution control. Limnologists also study ways to protect the wildlife that lives in lakes and rivers as well as the lakes and rivers themselves. Some limnologists are working on construction of artificial wetlands, which could serve as habitats for a variety of animal and plant species and aid in decreasing water pollution.

History of limnology

Limnology is a relatively new academic subject. Frangois-Alphonse Forel (1841-1912), considered the father of limnology, was a Swiss physician who dedicated much of his life to the study of the biology, chemistry, and physics of Lake Geneva. Around 1868, he coined the term limnology to mean the study of lakes. (The root word limn means "lake" and ology means "the study of.")

In 1887, American naturalist Stephen Alfred Forbes (1844-1930), a pioneer in the study of lake ecology (the study of the relationships between organisms and their environment), published the paper "Lake as a Microcosm," which is still cited as an important study of lake ecosystems. An ecosystem refers to all of the relationships between the living and nonliving parts of an environment.

Marine Archaeology

Many of the most famous archaeological sites are those of the ancient Egyptians, Greeks, Romans, and Vikings. While most all of these archaeological sites, from Egypt’s pyramids to Rome’s Coliseum, are on land, these cultures had strong ties to the sea, engaging in frequent trade and exploration. They also used ships in wars.

These civilizations left behind shipwrecks and the ruins of port cities that have been claimed by the sea due to erosion (wearing away of land). Technological advances in the late twentieth century permitted archaeologists to begin exploration and excavation of underwater archaeological sites. This branch of archaeology is called marine or underwater archaeology.

Archaeology explores how people lived in the past through excavation and survey. An excavation is a planned, careful exploration of ancient sites. It is sometime called a dig because digging (excavation) is the most well known method for discovering clues about the past at an archeological site. Wherever people live or work, they leave traces of their life.

Pieces of pottery, metal, glass, wood, bricks, and cut stone can remain behind for hundreds or thousands of years after a dwelling (house), city, or civilization has vanished. Remnants that were made or used by humans are called artifacts. Artifacts and their surroundings, called context, give scientists clues to what past peoples valued, what they ate, where they lived, and how they worked.

Marine Biology

Marine (ocean) biology is the study of the function, biodiversity, and ecology of the animals and plants that live in the ocean. An organism’s function is how it lives and grows in its environment. Biodiversity refers to the wide range of species of plants, animals, and microorganisms such as bacteria that live in the ocean.

Ecology is the study of the relationships between organisms as well as the relationships between organisms and their environment. In order to do their work, marine biologists incorporate information and techniques from a broad range of disciplines, including chemistry, physics, geology (the study of rocks), paleontology (the study of fossils), and geography (the study of locations on Earth).

Many factors make the marine environment a unique place for animals and plants to live. The marine environment is fluid, which affects the way organisms move and breathe. A variety of chemicals are dissolved in the water that bathes marine organisms and many have special ways to use these chemicals or to prevent them from entering their bodies. Ocean water is salty, which affects the organism’s ability to obtain and hold water in its body.

The ocean has relatively constant temperatures, especially compared to land. This means that animals do not need to exert a lot of energy to stay warm. Sunlight generally reaches only the surface layers of the oceans so plants must live in surface waters in order to perform photosynthesis (process where they convert energy from the Sun into food).

Marine Geology and Geophysics

Marine geology and geophysics are scientific fields that are concerned with solving the mysteries of the seafloor and Earth’s interior. Marine geologists, like all geologists, seek to understand the processes and history of the solid Earth, but their techniques differ from geologists who work on land because they study geologic (Earth’s) features that are underwater.

The oceans cover more than 70% of Earth, and water obscures a wealth of information about the rocks and sediments (particles of rock, sand, and other material) in the ocean basins. Marine geologists rely mainly on physical techniques to uncover the features and processes of the seafloor.

Geophysicists are scientists who study the physical properties of the solid Earth, and often work closely with marine geologists. Geophysicists use experiments and observations to determine how Earth materials such as rock, magma (molten rock), sediments, air, and water affect physical phenomena such as sound, heat, light, magnetic fields (a field of magnetic force), and earthquake tremors (seismic waves).

Marine geologists and geophysicists make images and maps of the seafloor, along with maps of sediment and rock layers below the seafloor. They also use instruments to measure changes in Earth’s gravity (the attraction between two masses), magnetic field, and the pattern of heat flow arising from deep in the Earth that help to explain geologic features of the ocean basins.


Oceanography, also called marine science, is the study of the ocean. Its goal is to discover unifying principles that can explain data measured in ocean waters, in the organisms that live in the ocean, and on the land surrounding the ocean. Oceanography is a broad subject, drawing on techniques and theories from biology, chemistry, physics, mathematics, geology, and engineering.

Oceanography is usually divided into four different areas of research. Marine biology or biological oceanography focuses on life (animals, plants, and bacteria) in the ocean. Chemical oceanography studies the substances that are dissolved in the ocean.

Physical oceanography attempts to understand the movement of water and the relationships between oceans and the atmosphere (mass of air surrounding Earth). Marine geology is directed at understanding geological features of the ocean floor, such as the composition of the seafloor and the movement of tectonic plates (moving plates of Earth’s crust).

Remote Sensing

Remote sensing is a technique that gives information about the surface of the Earth and the underwater world without touching the surface. The technique bounces energy off of nonliving or living objects and analyzes the returning signal to collect information.

Remote sensing has many uses in water. Common uses of remote sensing include charting the depth of a lake or ocean bottom. It is vital to the fishing industry and in locating objects at the bottom of the water. Treasure hunters and researchers would find it much harder to detect lost shipwrecks if not for remote sensing.

People interested in finding out where water pollution is occurring can take remote sensing images of water from planes or satellites (orbiting spacecraft) to detect microorganisms such as algae that thrive in polluted water. People who are trying to find deposits of oil and natural gas under the ocean floor also use remote sensing.

Agricultural Water Use

The images of seemingly endless crop fields of the American Midwest and the lush San Joaquin Valley of central California are powerful symbols of the agricultural might of the United States. In the past century, the United States has become the greatest producer of food in the world.

Water has always been a vital part of agriculture. Just like humans, crops need water to survive and grow. The process where dry land or crops are supplied with water is called irrigation. A century ago, the relatively small fields of a local farmer in many areas of the United States could receive enough moisture from rainwater, along with water that could be diverted from local streams, rivers, and lakes.

The growth of huge corporate farms that are thousands of acres in size has taken the need for water to another scale. For these operations, water needs to be trucked in, pumped up from underground, and obtained from surface water (freshwater located on the surface) sources in large quantities.

In modern times, in countries such as the United States and Canada, agriculture is not the largest user of water but is the largest consumer of water. Other activities such as the oil industry use more water than does agriculture. But, in these other industries, much of the water is put back into the ground or surface water after being used. Agriculture consumes water; the water does not go back to the surface or to the groundwater.


Aquaculture is the farming of animals or plants under controlled conditions in aquatic environments. Aquaculture usually refers to growing animals and plants in fresh or brackish water (water that has a salt content between that of freshwater and that of ocean water). Mariculture indicates the farming of animals and plants in ocean waters. (Marine means seawater.)

Just as on land, aquaculture and mariculture farmers try to control the environmental factors surrounding their crops in order to make them grow quickly and in good health. Some of the factors that aquaculture and mariculture farmers manipulate are the diet of their animals, the nutrients provided to their plants, the reproductive cycles of both animals and plants, and the chemistry and physical properties of the water where the farms are located.

They also try to develop methods to minimize diseases in their crops, to keep their crops safe from predators (animals that hunt them for food), and to reduce the pollution produced by their crops.

The aquaculture and mariculture industry

The combined industry of aquaculture and mariculture represents one of the fastest growing economic areas in the world. According to the United Nations Food and Agricultural Organization (FAO), aquaculture and mariculture have increased by nearly 10% per year since 1970.

Commercial and Industrial Uses of Water

Besides being vital for human survival, water is also necessary in commerce and in industry. Commercial operations are those that generally do not manufacture a product, but provide a service, such as hospitals, restaurants, and schools. Industry usually involves manufacturing a product.

In industry, water helps keep machinery needed for the making of products running smoothly and efficiently. Water can also be a vital part of the product, such as in sports drinks or soft drinks. In the United States, the total amount of fresh and salt water used every day by industry is nearly 410 billion gallons.

To illustrate such a huge number, think of that amount of water in terms of weight. A gallon of water weighs a little over 8 pounds (3.6 kilograms). The daily water usage in the United States totals almost 3.5 trillion pounds (1.6 trillion kilograms), about the same as 200 million 200-pound (90.7 kilogram) people!

Commercial water use

In modern day, water is essential to people’s daily lives. Without water, restaurants could not supply meals or even clean up after the meals, cars would go unwashed, and fires could be disastrous, with no means of dousing the blaze. Green parks, recreational fields, and golf courses rely on water to keep the grass and soil moist and healthy.

Economic Uses of Groundwater

Groundwater is one of humans’ most valuable natural resources. Groundwater is the water contained in the rock and soil layers beneath Earth’s surface, and it makes up most of Earth's supply of fresh, liquid water. (The oceans and ice in the North and South Poles contain 99% of Earth's total water supply. Groundwater accounts for almost all of the remaining 1%.)

Throughout history, humans have settled in areas with plentiful and pure groundwater, and have fought to own and protect wells and springs. Today, human water needs in many arid (dry) or heavily populated regions far exceed surface water supplies. Earth’s rapidly-growing human population is becoming increasingly reliant on groundwater.

Groundwater fills wells and city water supplies. Ground-water irrigates (waters) crops, feeds livestock, and produces farm-raised fish. Groundwater is used to cool nuclear reactors that generate electricity, mix concrete, and manufacture millions of consumer products. In short, groundwater plays a vital role in almost every facet of people’s lives, from drinking water, foods, and products people buy to roads and the buildings in which people live and work.

Groundwater reservoirs: aquifers

Water enters underground reservoirs by soaking in through soils, stream beds, and ponds in areas termed recharge zones. Water flows, often very slowly, through interconnected pore (tiny opening) spaces and then remerges onto the land surface at natural discharge points called springs and seeps.

Minerals and Mining

Minerals are defined as naturally occurring solids found in the earth that are composed of matter other than plants or animals. Ore is a naturally occurring source of minerals, such as a rock. A mineral can be composed from one element, such as diamond, which contains only carbon, or several elements, such as quartz, which contains silicon and oxygen. An element is a substance that cannot be divided by ordinary chemical means.

Even ice is considered a mineral. Minerals are found everywhere on Earth, from the bottom of the ocean to the highest mountains. Mineral deposits are frequently located underground, and thus they must be mined. South Africa and Russia hold the largest amount of minerals in the world. Minerals are vital to people’s lives, and many of these minerals are critical to countries’ industries and economies.

The United States is relatively poor in critical minerals, including platinum, cobalt, and gold, but there are sand deposits of titanium ore in Florida and the Pacific Northwest. In the central United States, minerals that contain lead and gallium (used in computer chips) are abundant, and iron ore is found in the states near the Great Lakes. Most of the diamonds are mined in Africa, as is gold, although gold is found in many other locations as well.

Importance of minerals

Minerals are essential in every aspect of life for humans. Humans need to ingest minerals in order for our bodies to function normally. Most of these required minerals come from the foods people eat. Gold and silver have been valued by civilization since ancient times.

Municipal Water Use

Many people live in municipalities (cities, towns, and villages with services such as water treatment, police, and fire department). One benefit of living in a municipality is that potable water (water safe to drink) is usually available at any time by turning on the tap. Part of the responsibility of citizens and municipal officials however, is to manage and protect the local water supply.

If municipal water becomes contaminated, the result can be far-reaching and rapid. Bacteria and viruses in water can spread throughout the underground reservoir of water (the aquifer) or throughout the miles of pipelines that carries water to houses in towns and cities. As well, non-living pollutants such as oil, gasoline and sediment can spread contaminate water.

The results of such contamination can be disastrous. In the summer of 2000, the municipal water supply of Walkerton, a town in the Canadian province of Ontario, became contaminated with a certain type of bacteria called Escherichia coli (or E. coli for short). This type of E. coli caused a serious illness in over a thousand people who drank the town water, and killed seven people.

In addition to protecting water for human use, water management also benefits the environment. Polluted water is bad for the many creatures that live in the water and depend on the watercourse in their lives.

Petroleum Exploration and Recovery

Petroleum, also called crude oil, is a thick, yellowish black substance that contains a mixture of solid, liquid, and gaseous chemicals called hydrocarbons. Since its discovery as an energy source in the mid-1800s, petroleum has become one of humans’ most valuable natural resources. Petroleum is arguably the single-most important product in the modern global economy.

Hydrocarbons separated (refined) from crude oil provide fuels and products that affect every facet of life in industrialized nations like the United States. Natural gas and propane are gaseous hydrocarbons that are used to heat homes and fuel stoves. Natural gas actually exists as a gas in underground reservoirs (underground rock formations containing oil or natural gas) and is not refined from crude oil, but it is still considered a petroleum product.

The liquid portion of petroleum becomes such essential products as home heating oil, automobile gasoline, lubricating oil for engines and machinery, and fuel for electrical power plants. Asphalt road surfaces, lubricating oils for machinery, and furniture wax are all composed of semi-solid hydrocarbons. Petroleum products are the building blocks of plastics. The hydrocarbon gas ethylene is even used to help ripen fruits and vegetables!

Oil and water don’t mix, but these two essential natural resources do have a lot in common. Naturally occurring petroleum forms from the chemical remains of organisms that lived and died in ancient seas. Petroleum collects in deeply buried rock layers called sedimentary rock that are, more often than not, the geologic remains of water-laid deposits like beds of sand or coral reefs on the sea floor. (Sediment is particles of rock sand or silt.)

Residential Water Use

In the United States, approximately 408 billion gallons (1,544 billion liters) of water are used every day! While power production and irrigation (watering crops) consume the majority of water usage, public and self-supply water systems produce 47 billion gallons (178 billion liters) a day for residential users and businesses.

Residential water use includes both indoor and outdoor household water usage. Water is used indoors for showering, flushing toilets, washing clothes, washing dishes, drinking, and cooking. Outdoor water usage includes washing the car, and watering the lawn, pools, and plants.

Public and private water

Nearly 85% of residential water users in the United States receive their water from public supply water systems. A public supply water system is a government facility or private company that collects water from a natural source such as a lake, river, or the ground.

Through a process called purification, pollutants, mud, and salt are removed from the water, and then the clean water is delivered to residents for a fee. Public water systems also remove wastewater, all water that goes down a drain, away from homes. Sewer systems carry wastewater to treatment plants where the water is cleaned and then released.


Common table salt is a compound. A compound is a chemical substance in which two or more elements are joined together. An element is a substance that cannot be broken down into a simpler substance. Elements, either alone or joined together as compounds, make up every object. The elements sodium and chlorine join together to make table salt.

Sodium is represented by the symbol "Na," and chlorine is represented by the symbol "Cl." Because one atom (smallest unit that has all the chemical and physical characteristics of an element) of sodium joins with one atom of chlorine, table salt is represented by the symbol "NaCl."

The need for salt

All animals, including humans, require salt. Salt is needed to regulate many bodily functions including maintaining a regular heart rhythm, blood pressure, and fluid balance in the body. Additionally, salt is required for nerve cells to communicate efficiently, and for regulating the electrical charges moving into and out of cells during processes such as muscle contraction.

An adult human has about 9 ounces (about 250 grams) of salt in the body. As the body cannot produce salt, animals must get salt from food and water. If too much salt is consumed, the kidneys remove the salt and flush it out of the body.

Shipping on Freshwater Waterways

For thousands of years humans have used freshwater waterways to ship food, building materials, and goods between regions. A freshwater waterway is any low-salt body of water, such as a river, lake, or man-made canal on which ships may travel. The need for freshwater for drinking and irrigation (watering crops) led most early civilizations to develop along rivers.

Shipping on freshwater waterways continues to be a reliable and important way to transport goods. Shipping goods over waterways is slower than other forms of shipping, yet it is less expensive and allows larger loads of cargo. Therefore many heavy raw materials such as coal, oil, timber, food products, and metal are often shipped over water. Many modern cities are still located along rivers and lakes.

Shipping in ancient Egypt

The ancient Egyptians (3000 b.c.e.-30 c.e.) depended upon the Nile River for their survival. The Nile River was the only source of drinking water for most Egyptians. Its yearly floods deposited silt (fine particles smaller than sand) that fertilized Egyptians crops. The Egyptians also used the Nile as their main highway, connecting Upper Egypt in the south with Lower Egypt in the north.

Shipping on the Oceans

Throughout recorded history, humans have relied on the oceans to ship goods quickly and efficiently. Historically, shipping on the oceans had several advantages over shipping over land. Shipping over land required moving bulky and heavy goods over mountains, across deserts, or through forests.

The location of roads often dictated where goods could be shipped. Before vehicles, land travelers also had to carry enough food and water to keep their pack animals alive, adding to the weight of their loads.

Two thousand years ago, the power of the Roman Empire was founded on the economic benefit that Rome gained from its control of trade on the Mediterranean Sea. Most of Rome’s empire lay on the shores of the Mediterranean Sea, which served as a highway for the trade of wine, food, timber, spices, and other valuable materials.

Surface and Groundwater Use

Surface water is the water that lies on the surface naturally as streams, rivers, marshes, lagoons, ponds, and lakes. Surface water can also be collected and stored in containers that have been built especially for that purpose. These containers are called reservoirs. Fresh water also collects in areas of soil and rock underground. This is groundwater.

Rain falling from the sky and snow melting in the springtime can flow downhill to gather in stream or riverbeds. From there, the water flows to a lake or ocean. In other locations, the rain or melted snow is soaked up by the soil and makes its way further down into the ground because of gravity (the force of attraction between all masses in the universe).

Uses of surface and groundwater

Surface water tends to be used by humans more often than groundwater. This is because it is much easier to obtain surface water. Inserting a pipe or tube into the water and then pumping out the water is all that is needed. Sometimes, if the surface water source is located on a hillside, the water flows through the pipeline because of gravity.

Tourism on the Oceans

Human interest in the sea fuels a multi-billion dollar a year ocean tourism industry. Ocean tourism refers to pleasure travel in which the sea is the primary focus of activities. Ocean tourism comes in many forms including cruises, ecotourism, and fishing expeditions.

Cruising the oceans

Cruises are one of the most popular forms of ocean tourism. In the late nineteenth and early twentieth century, cruise liners were needed to carry passengers across the oceans. Many of these cruise ships—including the ill-fated Titanic, which sank in 1912 killing over 1,500 people—provided passengers a luxurious way to travel. Originally powered by steam-driven engines, most modern cruise ships use diesel fuel to power their engines.

While cruise ships were needed for Atlantic Ocean crossings, by the mid-twentieth century, air travel made ocean crossings cheaper and faster. An airplane can cross the Atlantic in several hours instead of the one week required by most cruise ships. Cruise lines could no longer promote their services as providing a means of travel to and from vacation. (A cruise line is a company that owns one or more cruise ships.) With little need for cruise ships for ocean crossings, cruise line operators had to take a different approach to their business. They began to change the concept of the cruise itself to a vacation. Ships started traveling to exotic locations and offering more services and activities.

Today’s cruise ships are large ships that serve as floating hotels for vacationers. Cruise ships include restaurants, shops, swimming pools, theaters, and cinemas. Some cruise ships even offer college-level courses onboard. Cruise ships cost hundreds of millions of dollars to construct and may be over 1,000 feet (305 meters) long, over 150,000 gross tons (a term use to describe the size of a boat, ship, or barge), and stand taller than a 20-story building. The length of the largest cruise ship in 2004, the Queen Mary 2, is only 117 feet (36 meters) shorter than the height of the Empire State Building. The largest cruise ships can carry nearly 4,000 people, including the crew.

Transportation on the Oceans

For thousands of years, oceans provided one of the fastest and most valuable forms of transportation. By 3200 b.c.e., Egyptian ships made of reeds (tall, woody grass) used sails to travel along the coast of northern Africa. Over the centuries, ocean-going ships became larger and faster.

Around 1000 b.c.e. the Vikings explored the coast of Canada in sailboats. Spanish ships explored the Americas in the fifteenth and sixteenth centuries. British tall ships carried settlers to the Americas, Asia, Australia, and Africa in the sixteenth through nineteenth centuries.

Until the mid-twentieth century, ships were the only mode of transportation for ocean crossings. The rise of air transportation after 1930 reduced the role of ocean-going vessels in transportation. Airplanes provided a quicker and often cheaper way to move people great distances, which caused the types of vessels and purposes of ocean transportation to change.

Immigration to the New World

For the first 450 years after the discovery of the New World, ships provided the only form of transportation between Europe and the Americas. Nearly every citizen of the United States is descended from ancestors who traveled to the New World by ship, and immigration to the New World was a major factor in ocean transportation during this time.


Whaling, which is the hunting and killing of whales, is an activity that dates back centuries. Native people like the Macah, Nootka, and Coastal Salish of the Pacific Northwest are known to have hunted whales nearly 2,000 years ago. Whaling became popular with Europeans when they colonized North America in the late 1600s.

By 1672, whaling parties were organized off of Cape Cod in Massachusetts and off of Long Island in New York. However, by the early 1700s, the number of whales that close to shore had already begun to decline, so larger ships called sloops were developed that could capture whales farther off shore.

In the late 1800s, whaling had become a thriving commercial industry. Two of the most commonly hunted whales were the right whale and the sperm whale. The right whale was so named because it was the "right" whale to catch.

It floated after it was killed and so it was easy to recover from the ocean. Sperm whales were highly prized for their spermaceti, an oil found in their heads and used for making candles.

Dangerous Waters

Ever since humans first took to the seas thousands of years ago, sailors have faced numerous dangers. Ancient civilizations tried to explain these dangerous conditions by claiming that they were the work of angry gods or monsters.

While scientific explanations have been advanced for dangerous phenomena such as high waves, hurricanes, and treacherous ocean currents (steady flows of water in a prevailing direction), many lives are still lost in the water each year, mainly due to drowning or hypothermia.

Hypothermia is a condition where the core body temperature becomes too cold to function properly. Prolonged exposure to waters that may initially seem warm, between 70°-80°F (21°-27° C), can cause death from hypothermia.


Some of the earliest written works make references to the dangers of the seas. In the Odyssey, Greek poet Homer mentions a great whirlpool that a group of Greek warriors encountered on their return home from the Trojan War.

Recreation in and on Freshwaters

Fishing and swimming

Fishing is one of the most popular freshwater activities, with over 44 million anglers (people who fish) in the United States. Fish live in almost every lake, river, and stream in the United States, which makes fishing possible for most Americans.

There are two main types of freshwater fishing: fly fishing and spin fishing. The form of fishing used depends on location, the type of fish, and the body of water. Fly fishing is most popular on rivers and streams. Popular types of fish for freshwater fly fishing include trout, bass, and salmon.

When fly fishing, the weight of the fishing line carries the fly, or lure, out into the stream. A series of arm motions whip the fishing line overhead like a bullwhip, simulating the movement of the prey. Fly fishers lure fish with artificial flies and other artificial water-loving insects that are the natural prey of river fish.

In spin fishing, weights called sinkers are attached to the line and carry the hook and artificial lure out into the water. The hook then sinks in the water and the lure spins as the angler reels in the line impersonating an attractive meal to the fish. Trout, salmon, bass, and pike are popular targets for spin fishers.

Recreation in and on the Oceans

Every year, Americans spend billions of dollars and a large amount of their spare time on recreational activities in and on the oceans. Among others, popular ocean-based activities include swimming, snorkeling, scuba diving, sailing, fishing, and surfing.

In the ocean

Swimming is one of the most popular forms of ocean recreation. Millions of Americans visit the beach every year to swim in the ocean. While swimming, beachgoers participate in snorkeling. Snorkeling, or skin diving, is a form of diving in which the diver swims at or near the surface of the water.

Skin diving is simply holding one’s breath underwater for as long as possible. The diver can remain underwater for long periods by breathing through a snorkel, which is a hollow tube attached to a mouthpiece. The snorkel juts out above the surface of the ocean, allowing the diver to breathe surface air through the snorkel like a straw.

Arid Climates

An arid climate is one that receives less than 10 inches (25.4 centimeters) of rainfall in an entire year. Deserts are areas that are arid. Although the most familiar image of a desert involves hot sand, the Arctic North and Antarctica are also deserts, as they also receive little moisture, usually in the form of snow.

In contrast, the island of Fiji receives drenching rains for several months of the year, and is located in a tropical area of the world. Fiji receives an astounding 120 inches of rain each year, more than ten times the rainfall that falls in arid areas.

The rain that falls in an arid climate is sporadic and when it does fall, it is usually in the form of a thunderstorm. Flash floods are frequently a danger in arid climates after thunderstorms as the dry, compact soil cannot absorb water quickly enough to capture the rain. Streams swell with water for a few hours and then dry up again until the next cloudburst.

Plants surviving in an arid climate

Plants that survive in an arid climate have adapted to cope with the rare rainfall. Some plants can remain dormant (inactive) most of the time, only growing and reproducing when water is available. This cycle of activity and inactivity that is geared to the availability of water (and sometimes to other factors such as temperature) allows these hardy plants to survive for years.

Exploration of the Oceans

For centuries, exploration of the oceans was primarily limited to exploration on the surface of the oceans. Explorers sailed or rowed ships across the seas in search of new lands or natural resources.

Biological limits prevented humans from exploring beneath the surface. Three main issues prevented humans from exploring great depths of the ocean. First, humans must breathe air to survive, and humans can hold their breath for several minutes or less.

This does not provide much time to dive, explore, and return to the water’s surface. Second, the weight of water increases greatly as a diver descends into deep water. Finally, water temperature decreases with increasing depths. The temperature near the ocean floor is near freezing.

In the last half of the twentieth century, humans made great advancements in ocean exploration. Technological advancements greatly increased knowledge of marine biology (ocean life) and marine geology (ocean floor composition and structure). Humans and machines can now dive to great depths to explore the hidden world that lies below the surface of the ocean. Most of the vast ocean however, still remains unexplored.

Water and Cultures in the Ancient World

Water was the center of life in many ancient cultures. In Greek mythology, one of the most ancient and powerful gods was Neptune, the god of the sea. Ancient Greek literature, such as The Odyssey by Homer (about 800 b.c.e.), mentions sea monsters, whirlpools, and harrowing voyages upon the sea. In India, the Ganges River was considered sacred from historical accounts over 3000 years old.

To the ancient Egyptian, the Nile River was the political, economic, and life-sustaining center of their kingdom. Without the Nile, Egypt would be as barren as its nearby deserts. Ancient civilizations’ respect for water grew from their absolute need for water. Like today, water sustained life in many ways.

Seafaring in the ancient world

Ancient cities constructed beside the sea based their economies on the nearby water. Fishing, exploration, trade, and warfare necessitated shipbuilding. Shipbuilding was one of the most important crafts of the ancient world.

Most ships were wooden, but smaller boats used for fishing were sometimes made of bark or cured (dried and treated) animal skins. Making wooden ships required a good supply of timber and a means of transporting that timber to seaside shipyards. A shipyard is a place where ships are built and repaired.

Water and Cultures in the Modern World

Water plays an important role in shaping the modern world. Cities are built on water. Humans rely on water for cooking, drinking, washing, transportation, trade, energy, irrigation (watering crops), and recreation.

The use of water in the modern world has also created problems. Population growth and advancements in technology threaten the world’s water supply. Overfishing and pollution stress many of the world’s seas, and shortages of water stress human populations in arid (extremely dry) lands.

Cities and ports

Most cities are located beside water, Coastal areas in particular boast large cities. Eight out of the top ten most populous cities in the world lie on the coast. Nearly 44% of the world’s population lives within 100 miles (161 kilometers) of a coast.

Coastal cities grow because ports are an integral part of modern life. A port is place where people and merchandise can enter or leave a country by boat. Ports are essential for trade, or the movement of materials in exchange for money.


In countries like the United States, where some states are dotted with countless lakes and many people live within easy reach of an ocean, it may be easy to assume that drinking and recreational waters are limitless. This is not the case.

In many areas of the world, water is a preciously limited resource and in some cases, water scarcity is the result of human activity. In many countries in which the water supply is scare, water is being used faster than it is being renewed, often for agriculture or to supply water for a growing population.

Agricultural overuse

About 30% of all the freshwater used in the United States and 60% of the world’s available supply of freshwater is used to grow crops. Crops require a large volume of water for production. For example, to produce 2.2 pounds (1 kilogram) of rice requires about a bathtub full of water.

Only about half of the billions of gallons of water applied to crops each year makes it back to the surface or underground. The rest is lost to the air as evaporation (the change of water from liquid to vapor) and transpiration (evaporation of water from plant leaves), leaks, and spills.

Sediment Contamination

The bottom of streams, rivers, lakes, ponds, mudflats, and even oceans is made up of materials that were deposited there by the natural forces of currents (a constant flow of water in a predominant direction), gravity (attraction between two masses), and flows of incoming streams and rivers. This material, consisting of soil, pebbles, silt, clay and other material, is known as sediment.

Sedimentation (the deposit of sediments) becomes a problem if it is contaminated by toxic (poisonous) chemicals or harmful microorganisms. Just as soil and other material is carried to the bottom of water bodies, harmful chemicals or organisms can collect on the sediments.

The problem of sediment contamination is increasing in many areas throughout the world. The United States Environmental Protection Agency (EPA) conducted a survey across the country in 1998 in which they found hundreds of contaminated sites.

Many of these were located in coastal areas, which are rich habitats for plant and animal life. According to the EPA, every major harbor in the United States has some degree of contamination in the local sediment.

Species Introduction

Daily life in most environments, including the watery environments of salty oceans and freshwater streams, rivers, lakes, ponds, and wetlands is a balance between all the living things in the particular environment (ecosystem). Changing the mix of these living things can upset the ecosystem and have undesirable consequences.

Sometimes the change is accidental. A new species (a classification of related organisms that can reproduce) can happen to find its way into a new environment where the conditions include plenty of food, few enemies, and an ideal temperature.

The change can also be deliberate, due to humans’ attempts to control one undesirable species by adding another. Sometimes, the introduced species thrives in the environment and becomes the dominant species.

This can reduce the biodiversity (the vast range and number of different species) of the environment, as the introduced species outcompetes other species. But, this is not always the case. Species that are already present can adapt to the introduced species, survive, and even thrive.

Water Conservation

Conservation is the philosophy that natural resources should be used cautiously so that they will remain available for future generations of people. In practice, conservation is the act of protecting, managing, and restoring shared earth resources such as soil, air, forests, minerals, petroleum, wildlife, and water—one of humans’ most essential resources.

Water conservation can be as simple as one person using water sparingly during a drought (prolonged period of dry weather), or as complex as a multi-national committee de veloping a long-term water distribution plan for an entire continent.

The word conservation means different things to different people, and a workable conservation plan for a particular region or resource usually involves a compromise between several interest groups. Consider, for example, a forest. To a logging company, forest conservation means developing a system of cutting and replanting healthy, fast-growing trees that ensures continuing profits.

To a forest ecologist (a person who studies relationship between organisms and their environment) it means restoring a forest to a more natural state that supports a healthy community of plants and animals, along with protecting its most fragile areas and species. To a homeowner conservation means preserving the natural beauty of the forest and safeguarding property from forest fires. And to a preservationist it means letting nature manage the forest with little or no human intervention.

Water Pollution

Pollution is defined as the addition of harmful substances into the ecosystem (the network of interactions between living organisms and their environment). Pollutants might be slightly harmful to humans, but very harmful to aquatic life.

For instance, in certain lakes and rivers when acid rain (rain polluted with acidic chemicals) falls upon them, toxic (poisonous) metals that cause fish to die are released from sediments (particles of soil, sand, and minerals, and animal or plant matter washed from land into water). These metals—chromium, aluminum, and mercury are just a few—are harmful to fish.

But humans would have to ingest much larger quantities than the aquatic or marine life. The toxins also accumulate in the tissues of fish as they eat other fish (ingest) or plants containing toxins. If one were to catch and eat a fish that has a high content of toxins in them the human is affected too.

Metals are not the only pollutants that are of concern, as evidenced by oil spills hat kill marine life in large quantities and persist on beaches and in sediments for a long time. Industrial processes produce harmful waste, and often this is discharged into a nearby stream, river, or ocean. There are many ways to cause pollution and many types of pollutants.


A watershed is a connected series of streams, rivers, and lakes that collects water from a specific area of land. Watersheds are important habitats for animals and plants, and offer a source of drinking and recreational water for many communities.

The quality of the water in a watershed, also sometimes referred to as the health of the watershed, is important to preserve or remediate (to repair after damage). Water quality generally refers to the appearance, smell, and, above all, ability to serve as drinking water (a quality known as potability).

At the beginning of the twentieth century, most watersheds were unaffected by man-made pollution; pollution occurred only from natural sources such as animal waste. Before increased levels of man-made contamination, most watersheds were able to dilute pollutants or filter them out through surrounding wetlands (grassy areas that hold water throughout most of the year).

Today, pristine and uncontaminated watersheds are rarely observed. Pressures from modern urban development, mainly runoff of pollution and decreased air quality, make monitoring water quality a necessity.

Endangered Species Laws

A species (group of like organisms that can reproduce) is listed as endangered if it is in immediate danger of extinction throughout all or a significant part of its habitat. Fossils show that many plants and animals have become extinct over millions of years.

As of 2004, there are about 400 animals and 600 plants that are native to the United States listed as endangered. Over 125 animals and nearly 150 plants are currently listed as threatened. A species is listed as threatened if that species is likely to become endangered in the foreseeable future.

Many species of plants and animals become endangered and extinct naturally, usually due to changes in climate or loss of food sources. However, over the last several centuries, humans have posed a new threat to plants and animals. Human activities have resulted in the extinction of thousands of species.

Exclusive Economic Zones

For centuries, coastal nations have sought control over the oceans near their shores. These countries have also sought the right to control the ocean’s valuable resources as coastal nations have long valued coastal waters with large amounts of fish. Fishing is important for food and trade.

Coastal nations quickly realized that they must control and defend their coastal waters in order to protect their ocean resources. In modern day, countries have established exclusive economic zones, or EEZs. An EEZ gives a coastal nation the sole right to explore and extract all natural resources from the ocean for 200 miles (322 kilometers) off its shores. That nation also has the duty to conserve and responsibly use the ocean resources within its EEZ.

Establishing territorial waters

By the seventeenth century, laws governing the ocean began to develop. The ocean was divided into two categories: territorial waters and the open ocean. Territorial waters are the part of the ocean just off a nation’s coast over which that nation may exercise any right.

The nation in control of the territorial waters may defend those waters from other nations. Only the nation in control of its territorial waters could remove resources from those waters. The open ocean, or high seas, is the expansive, deep part of the ocean. Every nation had the right to travel over the open ocean and remove any resources.

Fishing, Commercial Regulation (Fresh and Salt Water)

Fishing regulations are government restrictions on where and how fish may be caught. Typically fishing regulations address the time of year, place, and how many fish of a certain type of fish may be caught. Commercial fishers have to follow many fishing regulations. A commercial fisher is a company that seeks to make a profit from the sale of fish.

Commercial fishing regulations are necessary

Worldwide, one out of every five people relies on fish as their primary source of protein. A decrease in fish populations could lead to malnutrition in human populations. Fishing is also economically important, as over 200 million people work in the fishing industry. Fishing regulation seek to minimize the decrease in fish populations and harm done to the ocean environment.

Overfishing. Until the mid-1800s humans did not have the ability or the need to catch extremely large numbers of fish.Advancements in fishing capabilities and technology changed this situation. In the mid-nineteenth century, steam powered ships began to replace sailboats. Steam ships could travel faster and remain at sea for long periods, catching more fish than sailboats. In the twentieth century, diesel powered ships replaced steam ships. Diesel ships could travel faster and farther than steam ships.

Steel and iron replaced wood as the primary building material for ships after about 1850. The use of steel and iron allowed ship builders to make larger ships capable of storing more catch. By 1950 fishing ships had become large, fast ships that could remain at sea for months at a time. These fishing ships used refrigeration to keep their enormous catches fresh for the voyage home. The invention of refrigeration and freezing units also allowed fish to be sent to areas far inland. Before refrigeration, only people who lived close to the coast could eat fish.

Nonprofit International Organizations

An international organization is a group that includes two or more countries and that operates in more than one country. Non-profit organizations operate for the public good, rather than for monetary gain.

Many international non-profit organizations share the latest techniques and knowledge about managing the water resources of the world. These international organizations focus mainly on improving the water supply, preventing and treating water pollution, and educating the public about conserving water.

A significant part of humanity, especially in developing countries, lives in areas where water is in short supply. Over 1 billion people in the world are without access to enough water, and over one-third of all people on Earth lack proper sanitation facilities, including the means to purify water and wastewater (water used by humans, animals, or industry). As a result, more than 3 million people die each year from diseases caused by contaminated water.

Reasons for water shortages

In large portions of Africa, Asia, and the Americas, the climate is usually arid (dry). Human life in desert and semi-desert regions of the world can be difficult due to lack of rain. Some regions of the Atacama Desert in Chile, for example, have not had rain for over 400 years!

International Water Laws and Enforcement

An international water law is an agreement between two or more nations that regulates activity on the seas. Most international laws come into effect after the participating nations sign a treaty. A treaty is an international agreement between two or more nations in written form and governed by international law.

United Nations Law of the Sea

Until the twentieth century, nations did not have the ability to protect their coastlines and waters for a great distance. Nations also did not require or have the ability to use vast amounts of ocean resources, such as fish or crude oil. For these reasons nations observed only a 3-mile (4.8-kilometer) territorial water zone until 1900. A territorial water zone is an area off the coast or on a nation’s border in which a nation can defend and enforce its laws.

By 1850, military progress enabled nations to defend waters far beyond the traditional 3 mile (4.8 kilometer) territorial waters. Modern fishing ships also had the ability to remain at sea for months at a time and catch tons of fish. These developments led many nations to consider extending their territorial waters.

After the discovery of oil and natural gas deposits under the ocean floor, the United States, in 1945, became the first nation to abandon the 3-mile (4.8 kilometer) territorial waters limit. Other nations soon joined the race to claim as much of the ocean and its resources as they could.


Aqueducts are man-made conduits constructed to carry water. The term aqueduct comes from words meaning "to lead water" in Latin, the language of the Romans who were the first builders of large aqueducts. Aqueducts carry water from natural sources, such as springs, into cities and towns for public use.

The first aqueducts

Wells, rivers, lakes, and streams are the oldest sources of water. In the ancient world however, rivers and lakes were also sometimes used as places to dispose of sewage and trash. Water from rivers that flowed though several villages often carried disease-causing organisms. Aqueducts provided a way for a plentiful supply of clean water to be piped into cities.

The earliest aqueducts were also used to transport water for irrigation (watering crops). Aqueducts were used in ancient India, Persia, Assyria, and Egypt as early as 700 b.c.e. The Romans, however, are regarded as the most famous ancient aqueduct builders.

Between 312 b.c.e. and 230 c.e., the most complex and efficient ancient system of aqueducts was built to supply the city of Rome with water. Outside of the capital city of Rome, the Romans built aqueducts throughout their large empire. Ruins of ancient aqueducts can still be seen in Italy, Greece, North Africa, Spain, and France.

Dams and Reservoirs

Dams are structures that restrict the flow of water in a river or stream. Both streams and rivers are bodies of flowing surface water driven by gravity that drain water from the continents.

Once a body of flowing surface water has been slowed or stopped, a reservoir or lake collects behind the dam. Dams and reservoirs exist in nature, and man-made water control structures are patterned after examples in the natural word.

Many lakes are held back by rock dams created by geologic events such as volcanic eruptions, landslides or the upward force of Earth that creates mountains. Humans and beavers alike have discovered how to modify their natural environment to suit their needs by constructing dams and creating artificial lakes.

Dams are classified into four main types: gravity, embankment, buttress, and arch.
  • Gravity dams: Gravity dams are massive earth, masonry (brick or stone work), rock fill, or concrete structures that hold back river water with their own weight. They are usually triangular with their point in a narrow gorge (deep ravine). The Grand Dixence dam in the Swiss Alps is the world’s tallest gravity dam.
  • Embankment dams: Embankment dams are wide areas of compacted earth or rock fill with a concrete or masonry core that contains a reservoir, while allowing for some saturation and shifting of the earth around the dam, and of the dam within the earth.
  • Buttress dams: Buttress dams have supports that reinforce the walls of the dam and can be curved or straight. Buttresses on large modern dams, such as the Itaipu dam in Brazil, are often constructed as a series of arches and are made of concrete reinforced with steel.
  • Arch dams: Arch dams are curved dams that depend on the strength of the arch design to hold back water. Like gravity dams, they are most suited to narrow, V-shaped river valleys with solid rock to anchor the structure. Arch dams, however, can be much thinner than gravity dams and use less concrete.


Approximately 97% of Earth’s water is either sea water or brackish water (a mixture of salt and fresh water). Humans and other animals cannot drink salt water and to do so can bring on dehydration (the loss of the body’s existing water) that can lead to illness and in extreme cases, death.

Desalination is the process of removing salt from seawater to make it drinkable (drinkable water is also called potable water) or to make it useable for irrigation (watering fields and crops).

Natural desalination occurs everyday as a part of the world’s hydrologic cycle. As salt water from the oceans evaporates (changes from liquid to gas), the salt is left behind and the water that moves into the atmosphere is fresh water. Thus, the water in clouds that eventually falls as rain is fresh water.

Salt can also be removed from water by a series of processes known as manipulated desalinization, desalting, or saline water reclamation (salt water reclamation). All of these man made processes are expensive in terms of how much money and energy they each require to produce a gallon of water.


Hydropower is energy that is generated by moving water. Today, hydropower facilities make electricity by converting kinetic (moving) energy into mechanical (machine) energy as water flows in a river or over a dam. Electricity made at hydropower facilities can be carried away, via power transmission lines, and sold to homes and businesses. Hydropower is a relatively inexpensive, non-polluting form of renewable energy.

Canada and the United States are currently the world’s top hydroelectric producers. Other countries that use hydropower on a large scale include Brazil, China, Russia, Norway, Japan, India, Iceland, Sweden, and France. Hydropower produces about 10% of United States’ electricity, in contrast to Norway, who generates nearly 99% of its electricity from hydropower.

Hydropower is used nationwide, but is primarily used in the western coastal United States where other energy resources such as coal are limited. Hydropower is important to the United States economy because it supplies electricity to a growing population and industry.

Hydropower in history

Humans have harnessed water power for thousands of years, using the mechanical energy of moving water to turn wooden wheels to power mills that sawed lumber and processed grains. Water either fell onto the wheel and caused it to turn or the wheel was placed in the river and the river’s current (a steady flow of water in a prevailing direction) turned the wheel. The wheel was attached to other levers and gears inside the mill that did the work needed.

Ports and Harbors

Peoples of ancient civilizations often built their cities on the shores of natural harbors. A harbor is place on the coastline that is protected from the full effects of tide and currents (a steady flow of ocean waters in a prevailing direction).

Harbors are often shaped like horseshoes. They are surrounded by land with a narrow opening through which ships can pass. Man-made harbors use structures such as walls or barriers built into the water to protect anchored ships from tide or storm damage.

Building cities near harbors permitted the construction of ports for trade. A port is a place on a shoreline for the loading and unloading of cargo from shipping vessels. Ports can be located on the ocean coast or on the shores of lakes and rivers. Cities with working ports are also called seaports or port cities.

Tide Energy

Tides are twice-daily rises and falls of water level relative to land. Ocean tides can produce strong currents (a steady flow of ocean waters in a prevailing direction) along some coastlines. Humans have sought to harness the kinetic (motion-induced) energy of the tides for hundreds of years.

Residents of coastal England and France have used tidal energy to turn water wheels and generate mechanical energy for grain mills since the eleventh century. In modern day, tidal currents are used to generate electricity.

Tidal energy is a non-polluting, renewable energy source. Modern day technologies for exploiting tidal energy are, however, relatively expensive and are limited to a few coastlines with extremely high and low tides. Tidal energy may, in the future, become more widely used and economically practical.

The power in tides

Tides result from the gravitational pulls of the Moon and Sun on the surface of the spinning Earth. Gravity is the force of attraction between all masses. The shape of the shore and adjacent seafloor affects the tidal range (difference between high and low tides) along specific coastlines.

Related Posts Plugin for WordPress, Blogger...