• river
    The Jinsha is nicknamed "the River of Golden Sands."

    Photograph by Xi Luo, MyShot

    Germ-Killing Ganges
    Hindus have always believed that the water of the Ganges River has purifying powers. Although millions of people bathe in the river regularly, it does not usually spread cholera, typhoid, or other water-borne diseases. Scientists have found that unique bacteriophagesviruses that destroy bacteriakill germs in the water of the Ganges.

    In addition, the Ganges holds up to 25 times more dissolved oxygen than any other river in the world. The oxygen helps prevent putrefaction (rotting) of organic matter in the river. Scientists do not know why the river retains so much oxygen.

    Mythical Rivers
    The ancient Greeks believed that five rivers encircled Hades, the underworld. These rivers are Styx (hate), Phlegethon (fire), Acheron (sorrow), Cocytus (lamentation or sadness), and Lethe (forgetting). The Greeks believed that dead souls had to cross the River Acheron, a branch of the Styx, to reach the underworld. They crossed on a ferry piloted by Charon, the ferryman of Hades.

    Flip-Flopping Flow
    The Amazon River used to flow in the opposite direction. Today, the river flows from the mountains of Peru in the west to the Atlantic Ocean in the east. But millions of years ago, it actually flowed from east to west, emptying into the Pacific Ocean. The flow flipped when the Andes mountains started growing at the end of the Cretaceous period (around 65 million years ago).

    A river is a large, natural stream of flowing water. Rivers are found on every continent and on nearly every kind of land. Some flow all year round. Others flow seasonally or during wet years. A river may be only kilometers long, or it may span much of a continent.

    The longest rivers in the world are the Nile in Africa and the Amazon in South America. Both rivers flow through many countries. For centuries, scientists have debated which river is longer. Measuring a river is difficult because it is hard to pinpoint its exact beginning and end. Also, the length of rivers can change as they meander, are dammed, or their deltas grow and recede.

    The Amazon is estimated to be between 6,259 kilometers (3,903 miles) and 6,800 kilometers (4,225 miles) long. The Nile is estimated to be between 5,499 kilometers (3,437 miles) and 6,690 kilometers (4,180 miles) long. There is no debate, however, that the Amazon carries more water than any other river on Earth. Approximately one-fifth of all the freshwater entering the oceans comes from the Amazon.

    Rivers are important for many reasons. One of the most important things they do is carry large quantities of water from the land to the ocean. There, seawater constantly evaporates. The resulting water vapor forms clouds. Clouds carry moisture over land and release it as precipitation. This freshwater feeds rivers and smaller streams. The movement of water between land, ocean, and air is called the water cycle. The water cycle constantly replenishes Earth’s supply of freshwater, which is essential for almost all living things.

    Anatomy of a River

    No two rivers are exactly alike. Yet all rivers have certain features in common and go through similar stages as they age.

    The beginning of a river is called its source or headwaters. The source may be a melting glacier, such as the Gangotri Glacier, the source of the Ganges River in Asia. The source could be melting snow, such as the snows of the Andes, which feed the Amazon River. A river’s source could be a lake with an outflowing stream, such as Lake Itasca in the U.S. state of Minnesota, the source of the Mississippi River. A spring bubbling out of the ground can also be the headwaters of a river. The source of the Danube River is a spring in the Black Forest of Germany.

    From its source, a river flows downhill as a small stream. Precipitation and groundwater add to the river’s flow. It is also fed by other streams, called tributaries. For instance, the Amazon River receives water from more than 1,000 tributaries. Together, a river and its tributaries make up a river system. A river system is also called a drainage basin or watershed. A river’s watershed includes the river, all its tributaries, and any groundwater resources in the area.

    The end of a river is its mouth. Here, the river empties into another body of water—a larger river, a lake, or the ocean. Many of the largest rivers empty into the ocean.

    The flowing water of a river has great power to carve and shape the landscape. Many landforms, like the Grand Canyon in the U.S. state of Arizona, were sculpted by rivers over time. This process is called weathering or erosion.

    The energy of flowing river water comes from the force of gravity, which pulls the water downward. The steeper the slope of a river, the faster the river moves and the more energy it has.

    The movement of water in a river is called a current. The current is usually strongest near the river’s source. Storms can also increase the current. A swift current can move even large boulders. These break apart, and the pieces that are carried in the moving water scrape and dig into the river bottom, or bed.

    Little by little, a river tears away rocks and soil along its bed, and carries them downstream. The river carves a narrow, V-shaped valley. Rapids and waterfalls are common to rivers, particularly near their sources.


    Eventually, the river flows to lower land. As the slope of its course flattens, the river cuts less deeply into its bed. Instead, it begins to wind from side to side in looping bends called meanders. This action widens the river valley.

    At the same time, the river begins to leave behind some of the rocks, sand, and other solid material it collected upstream. This material is called sediment. Once the sediment is deposited, it is called alluvium. Alluvium may contain a great deal of eroded topsoil from upstream and from the banks of its meanders. Because of this, a river deposits very fertile soil on its flood plain. A flood plain is the area next to the river that is subject to flooding.

    The deepest part of a river bed is called a channel. The channel is usually located in the middle of a river. Here, the current is often strong. In large rivers, ships travel in channels. Engineers may dredge, or dig, deeper channels so more water can flow through the river or the river can transport larger ships.

    Near the end of its journey, the river slows and may appear to move sluggishly. It has less energy to cut into the land, and it can no longer carry a heavy load of sediment. Where the river meets the ocean or a lake, it may deposit so much sediment that new land, a delta, is formed.

    Not all rivers have deltas. The Amazon does not have a true delta, for instance. The strength of the tides and currents of the Atlantic Ocean prevent the build-up of sediment. Deltas almost always have fertile soil. The Nile Delta and the Ganges Delta are the chief agricultural areas for Egypt and Bangladesh, for instance.

    Rivers Through History

    Rivers have always been important to people. In prehistoric times, people settled along the banks of rivers, where they found fish to eat and water for drinking, cooking, and bathing.

    Later, people learned that the fertile soil along rivers is good for growing crops. The world’s first great civilizations arose in the fertile flood plains of the Nile in Egypt, the Indus in southern Asia, the Tigris and the Euphrates in the Middle East, and the Huang (Yellow) in China.

    Centuries later, rivers provided routes for trade, exploration, and settlement. The Volga River in Eastern Europe allowed Scandinavian and Russian cultures, near the source of the river, to trade goods and ideas with Persian cultures, near the mouth of the Volga in southern Europe. The Hudson River in the U.S. state of New York is named after English explorer Henry Hudson, who used the river to explore what was then the New World.

    When towns and industries developed, the rushing water of rivers supplied power to operate machinery. Hundreds of factories operated mills powered by the Thames in England, the Mississippi in the United States, and the Ruhr in Germany.

    Rivers remain important today. If you look at a world map, you will see that many well-known cities are on rivers. Great river cities include New York City, New York; Buenos Aires, Argentina; London, England; Cairo, Egypt; Kolkata, India; and Shanghai, China. In fact, rivers are usually the oldest parts of cities. Paris, France, for instance, was named after the Iron Age people known as the Parisii, who lived on the islands and banks of the Seine River, which flows through the city.

    Rivers continue to provide transportation routes, water for drinking and for irrigating farmland, and power for homes and industries.

    Rivers of Europe

    The longest river in Europe is the Volga. It flows approximately 3,685 kilometers (2,290 miles) across Russia and empties into the Caspian Sea. The Volga has been used for centuries to transport timber from northern forests, grain from farms along its valley, and manufactured goods. The river is also known for its sturgeon, a type of large fish whose eggs are used to make a famous delicacy—Russian caviar.


    The Thames, in England, is one of Europe’s most historic rivers. Along its banks stands the city of London, a bustling urban area for more than a thousand years. By 100 CE, London had already become an important Roman settlement and trading post. Because of its location on the river and near the seacoast, London became England’s principal city and trade center.

    Europe’s busiest river is the Rhine, which runs from the Alps in Switzerland, through Germany and the Netherlands, and empties into the North Sea. It flows through many industrial and farming regions and carries barges laden with farm products, coal, iron ore, and a variety of manufactured goods.

    Rivers of Asia

    Asia’s longest and most important river is the Yangtze, in China. It flows from the Dangla Mountains, between Tibet and China’s Qinghai province. It empties in the East China Sea 6,300 kilometers (3,915 miles) later. The Yangtze is a highway for trade through the world’s most populous country.

    The Yangtze is also an agricultural river. Its valley is a major rice-growing region, and its water is used to irrigate fields. Many Chinese live on the river in houseboats or sailboats called junks.

    The Yangtze River is the home of the world’s most powerful hydroelectric power plant, the Three Gorges Dam. Eventually, the plant will be able to constantly produce 22,500 megawatts of power. China’s rural population will have access to affordable electricity for homes, businesses, schools, and hospitals. Creating the Three Gorges Dam was one of the largest engineering feats in history. Engineers dammed the Yangtze, creating a 39.3-cubic-kilometer (31.9 million acre-foot) reservoir, or artificial lake.

    The Ganges is the greatest river on Asia's Indian subcontinent. It is sacred to the millions of followers of the Hindu religion. For thousands of years, Hindus have worshipped the river as a goddess, Ganga Ma (Mother Ganges). Hindus believe the river’s water purifies the soul and heals the body. Millions of people use the Ganges every day for bathing, drinking, and industry.

    The historic Tigris and Euphrates river system flows from Turkey through Syria and Iraq and into the Persian Gulf. The rivers lie in an area called the Fertile Crescent. The region between the two rivers, known as Mesopotamia, is the so-called “cradle of civilization.” The earliest evidence of civilization and agriculture—farming and domestication of animals—appears in the Fertile Crescent.

    Rivers of North America

    In North America, rivers served as highways for native tribes and, later, for European explorers.

    French explorers began traveling the St. Lawrence and other rivers of Canada in the 1500s. They found an abundance of fish and other wildlife, and they encountered Native American tribes who hunted beaver. The explorers took beaver pelts back to Europe, where they were used to make fashionable hats. Soon, hunters explored and traveled networks of rivers in North America in search of beaver pelts. The establishment of trading posts along the rivers later opened the way for permanent European settlers.

    The St. Lawrence River is still a major waterway. The river, which empties into the Atlantic, is linked to the Great Lakes by the St. Lawrence Seaway—a series of canals, locks, dams, and lakes. The St. Lawrence Seaway allows oceangoing ships to enter the interior of the continent.

    The Mississippi is the chief river of North America. It flows approximately 3,766 kilometers (2,340 miles) through the heart of the United States, from its source in Minnesota to its delta in Louisiana and the Gulf of Mexico.

    Spanish and French explorers first traveled the Mississippi in the 1500s and 1600s. In 1803, the United States bought almost the entire Mississippi River Valley from France as part of the Louisiana Purchase. After that, the Mississippi was widely traveled by traders and settlers on rafts, boats, and barges.

    With the introduction of the steamboat, a new, industrial, era began on the Mississippi. Paddle wheelers carried trade goods up and down the river. Soon, workboats were joined by cruise ships and other luxurious passenger vessels. Writer Mark Twain, who was once a steamboat pilot on the river, described this era in his book Life on the Mississippi.

    Over time, the Mississippi increased in importance as a trade route. Today, it carries cargo ships and barges in lines that may extend for more than a kilometer. Large quantities of petroleum, coal, and other bulky goods are conveyed on the river by massive barges pushed by powerful towboats.

    North America’s Colorado River is famous for forming the Grand Canyon in Arizona. For millions of years, the river has cut its way through layers of rock to carve the canyon. Long ago, the river flowed through a flat plain. Then the Earth’s crust began to rise, lifting the land. The river began cutting into the land. The Grand Canyon is now about one and a half kilometers (one mile) deep at its deepest point, and 29 kilometers (18 miles) wide at its widest.

    Rivers of South America

    The strength of the Amazon River in South America dwarfs all other rivers on the planet. The amount of water flowing through the Amazon is greater than the amount carried by the Mississippi, the Yangtze, and the Nile combined.

    The Amazon begins as an icy stream high in the Andes mountains of Peru. It flows through Brazil and empties into the Atlantic Ocean. The Amazon and its tributaries drain a basin that covers an area equal to three-fourths of the contiguous United States.

    The first Europeans to see the Amazon were Spanish explorers, who traveled it in the 1500s. They encountered a group of natives who all appeared to be women, or so the story goes. The explorers called the people Amazons, after female warriors described in Greek mythology. The name Amazon was later given to the river.

    For much of its course, the Amazon flows through the world’s largest tropical rain forest. The region has abundant and unusual wildlife, including flesh-eating fish called piranhas; huge fish called pirarucu, which can weigh more than 125 kilograms (275 pounds); and giant snakes called anacondas.

    Some Amazon tribes remain independent of Western culture. The Tagaeri people, for instance, continue to live a nomadic life based around the Amazon and its tributaries in the rain forest of Ecuador. Because of the demand for timber from the rain forest, the land of the indigenous people of the Amazon is shrinking. Today, there are fewer than 100 Tagaeri living in the rain forest.

    Rivers provide energy to many South American communities. The Itaipú Dam crosses the Paraná River on the Brazil-Paraguay border. Construction of the dam required the labor of thousands of workers and cost more than $12 billion. The dam’s power plant can regularly produce some 12,600 megawatts of electricity. The huge reservoir formed by the dam supplies water for drinking and for irrigation.

    Rivers of Africa

    Africa’s two largest rivers are the Nile and the Congo.

    One tributary of the Nile, the White Nile, flows from tiny streams in the mountains of Burundi through Lake Victoria, Africa’s largest lake. The other tributary, the Blue Nile, begins in Lake Tana, Ethiopia. The two join at Khartoum, Sudan. The Nile then flows through the Sahara Desert in Sudan and Egypt, and empties into the Mediterranean Sea. Because the area where the tributaries meet is close to the two sources of the Nile, the area is called the Upper Nile, even though it is farther south geographically. The Lower Nile runs through Egypt.


    One of the earliest civilizations in the world developed along the Lower Nile. Ancient Egyptian civilization arose about 5,000 years ago. It was directly related to the Nile and its annual flooding. Each year, the river overflowed, spreading rich sediment across its broad flood plain. This made the land extremely fertile. Egyptian farmers were able to grow plentiful crops. In fact, ancient Egyptians called their land Kemet, which means “Black Land,” because of the rich, black soil deposited by the river.

    Egyptians also used the Nile as a major transportation route to both the Mediterranean and the African interior. The Pschent, or double crown worn by Egyptian monarchs, combined symbolism from both the Upper Nile and Lower Nile. A tall, white crown shaped like a bowling pin represented the lands of the Upper Nile. This crown was combined with a pointy red crown that had a curly wire protruding from the front. The red color symbolized the red soils of Lower Egypt, while the curly wire represented a honeybee. When putting on the Pschent, an Egyptian ruler assumed leadership for the entire Nile.

    The Nile provided enterprising Egyptians with material to form a powerful civilization. From papyrus, a tall reed that grew in the river, Egyptians made a sort of paper, as well as rope, cloth, and baskets. Egyptians also built great cities, temples, and monuments along the river, including tombs for their monarchs, or pharaohs. Many of these ancient monuments are still standing.

    The Congo River flows across the middle of Africa, through a huge equatorial rain forest, before emptying in the Atlantic Ocean. The Congo is second only to the Amazon in terms of water flow. It is the deepest river in the world, with measured depths of more than 230 meters (750 feet). Huge urban areas, including the capital cities of Brazzaville, Republic of Congo, and Kinshasa, Democratic Republic of Congo, sit on the banks of the river.

    In the Democratic Republic of Congo, the river is the principal highway for transporting goods such as cotton, coffee, and sugar. Boats traveling the river range from dugout canoes to large freighters.

    The river also supplies an abundance of fish to central Africa. Fishermen use baskets and nets hung from high poles across rushing falls and rapids to catch fish. They also use more traditional nets operated from either onshore or on boats.

    Rivers of Australia

    Much of Australia is arid, but rivers still run through it. Australia’s principal rivers are the Murray and the Darling, both in the southeastern part of the continent. The Murray flows some 2,590 kilometers (1,610 miles) from the Snowy Mountains to a lagoon on the Indian Ocean. Near the town of Wentworth, the Murray is joined by the Darling, a 2,739-kilometer (1,702-mile) river that flows from the highlands of the eastern coast.

    Indigenous Australians placed great importance on the Murray River. The Murray valley had the greatest population density on the continent before the arrival of Europeans in the 1600s.

    By the mid-1800s, European farmers had settled along both rivers and some of their tributaries. Most Australian farmers raised sheep and cattle. Riverboats began plying the waters, and towns grew up along the banks.

    Much of Australia’s farmland still lies within the Murray-Darling basin, where river water irrigates some 1.2 million hectares (3 million acres). The region is the chief supplier of the country’s agricultural exports—wool, beef, wheat, and oranges.

    Polluted Rivers

    For centuries, people have depended on rivers for many things. Rivers have provided waterways for shipping, convenient construction sites for cities, and fertile land for farming. Such extensive use of rivers has contributed to their pollution. River pollution has come from directly dumping garbage and sewage, disposal of toxic wastes from factories, and agricultural runoff containing fertilizers and pesticides.


    By the 1960s, many of the world’s rivers were so polluted that fish and other wildlife could no longer survive in them. Their waters became unsafe for drinking, swimming, and other uses. One of the most famous examples of a polluted river was the Cuyahoga. The Cuyahoga is a busy river in the U.S. state of Ohio that empties into Lake Erie. It is a major highway for goods and services from the Midwest to the Great Lakes. In 1969, the oily pollution in the Cuyahoga was so great that the river actually caught fire—something it had done more than a dozen times in the 19th and 20th centuries.

    Since the 1969 fire, stricter laws have helped clean up polluted rivers. The laws have restricted the substances factories can dump into rivers, limited the amount of agricultural runoff, banned toxic pesticides such as DDT, and required treatment of sewage.

    Although the situation in some parts of the world has improved, serious problems remain. The Citarum River in Indonesia, for instance, is often cited as the most polluted river in the world. Textile factories near the Citarum dump toxic wastes into the river. The garbage floating on top of the river is so thick that water is invisible.

    Even after communities have limited river pollution, toxic chemicals may remain. Many pollutants take years to dissolve. The pollutants also build up in the river’s wildlife. Toxic chemicals may cling to algae, which are eaten by insects or fish, which are then eaten by larger fish or people. At each stage of the river’s food web, the amount of the toxic chemical increases.

    In parts of North America and Europe, there is also the severe problem of acid rain. Acid rain develops when emissions from factories and vehicles mix with moisture in the air. The acid that forms can be toxic for many living things. Acid rain falls as rain and snow. It builds up in glaciers, streams, and lakes, polluting water and killing wildlife.

    Environmentalists, governments, and communities are trying to understand and solve these pollution problems. To provide safe drinking water and habitats where fish and other wildlife can thrive, rivers must be kept clean.

    Dams

    A dam is a barrier that stops or diverts the flow of water along a river. Humans have built dams for thousands of years.

    Dams are built for many purposes. Some dams prevent flooding or allow people to develop or “reclaim” land previously submerged by a river. Other dams are used to change a river’s course for the benefit of development or agriculture. Still others provide water supplies for nearby rural or urban areas. Many dams are used to provide electricity to local communities.

    In 1882, the world’s first hydroelectric power plant was built on the Fox River in the U.S. city of Appleton, Wisconsin. Since then, thousands of hydroelectric plants have been built on rivers all over the world. These plants harness the energy of flowing water to produce electricity. About 7 percent of all power in the United States, and 19 percent of power in the world, comes from hydroelectric plants. China is the world’s largest producer of hydroelectric power.

    Hydroelectric power is renewable because water is constantly replenished through precipitation. Because hydroelectric plants do not burn fossil fuels, they do not emit pollution or greenhouse gases. However, hydroelectric power does have some negative effects on the environment.

    Dams and hydroelectric plants change the flow and temperature of rivers. These changes to the ecosystem can harm fish and other wildlife that live in or near the river. And although hydroelectric plants do not release greenhouse gases, rotting vegetation trapped in the dams’ reservoirs can produce them. Decaying plant material emits carbon dioxide, a major greenhouse gas, into the atmosphere.

    Dams also have an effect on people living near the rivers. For example, more than 1.3 million people had to move from their homes to make way for China’s Three Gorges Dam and its reservoir. Human rights organizations claim that many of these people did not receive the compensation they were promised in return for being displaced.


    In addition, dams can affect fish populations and the fertility of flood plains. Fish may not be able to migrate and spawn. Farmers that depended on the fertile flooding may be cut off from the river by a dam. This can harm the livelihood of fishermen and farmers who live along the river, as well as consumers who must pay higher prices for food.

    Dams with very large reservoirs may also trigger earthquakes. Earthquakes happen when two or more of the tectonic plates that make up Earth’s crust slide against each other. The weight of the water in the reservoirs can cause existing cracks, or faults, in these plates to slip and create an earthquake.

    River Management

    River management is the process of balancing the needs of many stakeholders, or communities that depend on rivers. Rivers provide natural habitats for fish, birds, and other wildlife. They also provide recreation areas and sporting opportunities such as fishing and kayaking.

    Industries also depend on rivers. Rivers transport goods and people across continents. They provide affordable power for millions of homes and businesses.

    Farmers and agribusinesses often rely on rivers for transportation. Rivers also supply water for irrigation.

    River managers must consider the needs of all the current and future stakeholders.

  • Term Part of Speech Definition Encyclopedic Entry
    abundance Noun

    large amount.

    acid rain Noun

    precipitation with high levels of nitric and sulfuric acids. Acid rain can be manmade or occur naturally.

    agribusiness Noun

    the strategy of applying profit-making practices to the operation of farms and ranches.

    agriculture Noun

    the art and science of cultivating the land for growing crops (farming) or raising livestock (ranching).

    Encyclopedic Entry: agriculture
    algae Plural Noun

    (singular: alga) diverse group of aquatic organisms, the largest of which are seaweeds.

    alluvium Noun

    gravel, sand, and smaller materials deposited by flowing water.

    Amazon Noun

    in ancient Greek mythology, a woman belonging to a tribe of all-female warriors.

    anaconda Noun

    very large snake native to South America.

    annual Adjective

    yearly.

    arid Adjective

    dry.

    bacteria Plural Noun

    (singular: bacterium) single-celled organisms found in every ecosystem on Earth.

    bacteriophage Noun

    virus that infects bacteria.

    barge Noun

    large, flat-bottomed boat used to transport cargo.

    Blue Nile Noun

    tributary of the Nile River flowing from Lake Tana in Ethiopia and meeting the White Nile at Khartoum, Sudan, to form the Nile River.

    boulder Noun

    large rock.

    bustling Adjective

    busy.

    canal Noun

    artificial waterway.

    canyon Noun

    deep, narrow valley with steep sides.

    Encyclopedic Entry: canyon
    carbon Noun

    chemical element with the symbol C, which forms the basis of all known life.

    cargo Noun

    goods carried by a ship, plane, or other vehicle.

    caviar Noun

    delicacy made from the eggs of sturgeon or other fish.

    channel Noun

    deepest part of a shallow body of water, often a passageway for ships.

    Charon Noun

    in ancient Greek mythology, the ferryman who transported the souls of the dead across the river Styx and to the underworld, Hades.

    cholera Noun

    infectious, sometimes fatal disease that harms the intestines.

    civilization Noun

    complex way of life that developed as humans began to develop urban settlements.

    Encyclopedic Entry: civilization
    cloud Noun

    visible mass of tiny water droplets or ice crystals in Earth's atmosphere.

    Encyclopedic Entry: cloud
    coal Noun

    dark, solid fossil fuel mined from the earth.

    compensation Noun

    fee or money paid for goods, services, debt, loss, injury, or suffering.

    consumer Noun

    organism on the food chain that depends on autotrophs (producers) or other consumers for food, nutrition, and energy.

    contiguous Adjective

    land, space, or features that are in direct contact.

    continent Noun

    one of the seven main land masses on Earth.

    Encyclopedic Entry: continent
    crop Noun

    agricultural produce.

    Encyclopedic Entry: crop
    crown Noun

    headgear worn by a monarch or other ruler.

    cruise ship Noun

    vessel transporting tourists on a trip.

    current Noun

    steady, predictable flow of fluid within a larger body of that fluid.

    Encyclopedic Entry: current
    dam Verb

    to block a flow of water.

    DDT Noun

    (dichloro-diphenyl-trichloroethane) toxic chemical used as an insecticide but illegal for most uses in the U.S. since 1972.

    decay Verb

    to rot or decompose.

    delicacy Noun

    food or dish notable for its rarity or cost.

    delta Noun

    the flat, low-lying plain that sometimes forms at the mouth of a river from deposits of sediments.

    Encyclopedic Entry: delta
    development Noun

    construction or preparation of land for housing, industry, or agriculture.

    dissolved oxygen Noun

    measure of the amount of oxygen in a substance, usually water.

    domestication Noun

    the process of adapting wild plants or animals for human use.

    Encyclopedic Entry: domestication
    drainage basin Noun

    an entire river system or an area drained by a river and its tributaries. Also called a watershed.

    dredge Verb

    to remove sand, silt, or other material from the bottom of a body of water.

    dugout canoe Noun

    small boat made by hollowing out a log or tree trunk.

    dwarf Verb

    to make something appear small by having it appear next to something much larger.

    earthquake Noun

    the sudden shaking of Earth's crust caused by the release of energy along fault lines or from volcanic activity.

    ecosystem Noun

    community and interactions of living and nonliving things in an area.

    Encyclopedic Entry: ecosystem
    electricity Noun

    set of physical phenomena associated with the presence and flow of electric charge.

    emission Noun

    discharge or release.

    engineering Noun

    the art and science of building, maintaining, moving, and demolishing structures.

    equatorial Adjective

    having to do with the equator or the area around the equator.

    erosion Noun

    act in which earth is worn away, often by water, wind, or ice.

    Encyclopedic Entry: erosion
    evaporate Verb

    to change from a liquid to a gas or vapor.

    exploration Noun

    study and investigation of unknown places, concepts, or issues.

    export Noun

    good or service traded to another area.

    extensive Adjective

    very large.

    factory Noun

    one or more buildings used for the manufacture of a product.

    farm Noun

    land cultivated for crops, livestock, or both.

    fault Noun

    a crack in the Earth's crust where there has been movement.

    feat Noun

    accomplishment or achievement.

    ferry Noun

    boat or ship that transports people, cargo, and goods across a waterway.

    fertile Adjective

    able to produce crops or sustain agriculture.

    Fertile Crescent Noun

    region extending from the eastern Mediterranean coast through Southwest Asia to the Persian Gulf.

    fertilizer Noun

    nutrient-rich chemical substance (natural or manmade) applied to soil to encourage plant growth.

    flood plain Noun

    flat area alongside a stream or river that is subject to flooding.

    Encyclopedic Entry: flood plain
    food web Noun

    all related food chains in an ecosystem. Also called a food cycle.

    Encyclopedic Entry: food web
    fossil fuel Noun

    coal, oil, or natural gas. Fossil fuels formed from the remains of ancient plants and animals.

    freighter Noun

    large ship used for carrying heavy cargo, or freight.

    freshwater Noun

    water that is not salty.

    garbage Noun

    trash or waste material.

    glacier Noun

    mass of ice that moves slowly over land.

    Encyclopedic Entry: glacier
    grain Noun

    harvested seed of such grasses as wheat, oats, and rice.

    Encyclopedic Entry: grain
    gravity Noun

    physical force by which objects attract, or pull toward, each other.

    Great Lakes Noun

    largest freshwater bodies in the world, located in the United States and Canada. Lake Huron, Lake Ontario, Lake Michigan, Lake Erie, and Lake Superior make up the Great Lakes.

    greenhouse gas Noun

    gas in the atmosphere, such as carbon dioxide, methane, water vapor, and ozone, that absorbs solar heat reflected by the surface of the Earth, warming the atmosphere.

    groundwater Noun

    water found in an aquifer.

    Encyclopedic Entry: groundwater
    headwater Noun

    source of a river.

    hectare Noun

    unit of measure equal to 2.47 acres, or 10,000 square meters.

    Henry Hudson Noun

    (died 1611) English explorer and navigator.

    Hindu Noun

    religion of the Indian subcontinent with many different sub-types, most based around the idea of "daily morality."

    honeybee Noun

    insect that, in a hive with other honeybees, produces honey.

    houseboat Noun

    large, flat-bottomed boat used for residence but not suitable for open water.

    human rights Noun

    basic freedoms belonging to every individual, including the rights to social and political expression, spirituality, and opportunity.

    hydroelectric power Noun

    usable energy generated by moving water converted to electricity.

    indigenous Adjective

    native to or characteristic of a specific place.

    iron Noun

    chemical element with the symbol Fe.

    Iron Age Noun

    last of the prehistoric "three ages," following the Stone Age and the Bronze Age, marked by the use of iron for industry.

    irrigate Verb

    to water.

    junk Noun

    sailboat with square sails and, usually, a flat bottom, used mostly in and around China.

    labor Noun

    work or employment.

    laden Adjective

    full or heavy with.

    lagoon Noun

    shallow body of water that may have an opening to a larger body of water, but is also protected from it by a sandbar or coral reef.

    Encyclopedic Entry: lagoon
    lake Noun

    body of water surrounded by land.

    lock Noun

    structure on a waterway where gates at each end allow the water level to raise and lower as they are opened and closed.

    Louisiana Purchase Noun

    (1803) land bought by the United States from France, extending from the Mississippi River to the Rocky Mountains, and Canada to the Gulf of Mexico.

    Lower Nile Noun

    northern section of the Nile River.

    luxurious Adjective

    rich or self-indulgent.

    machinery Noun

    mechanical appliances or tools used in manufacturing.

    Mark Twain Noun

    (1835-1910, born Samuel Langhorne Clemens) American writer.

    meander Noun

    large curve in a lake or stream.

    meander Verb

    to wander aimlessly.

    Mesopotamia Noun

    area between the Tigris and Euphrates River in Iraq.

    Midwest Noun

    area of the United States consisting of the following states: Illinois, Indiana, Iowa, Kansas, Michigan, Minnesota, Missouri, Nebraska, North Dakota, Ohio, South Dakota, and Wisconsin.

    migrate Verb

    to move from one place or activity to another.

    mill Noun

    machine used for grinding or crushing various materials.

    monarch Noun

    king or queen.

    mouth Noun

    place where a river empties its water. Usually rivers enter another body of water at their mouths.

    Encyclopedic Entry: mouth
    myth Noun

    legend or traditional story.

    New World Noun

    the Western Hemisphere, made up of the Americas and their islands.

    nomad Noun

    person who moves from place to place, without a fixed home.

    ore Noun

    deposit in the Earth of minerals containing valuable metal.

    Encyclopedic Entry: ore
    paddle wheeler Noun

    steamboat used mostly on rivers propelled by one or more large wheels outfitted with paddles or scoops.

    papyrus Noun

    aquatic plant native to the Mediterranean Sea.

    Parisii Noun

    Iron Age people and culture native to the banks of the Seine River.

    pelt Noun

    animal skin or fur.

    Persia Noun

    empire that dominated Mesopotamia from about 550 to 330 BCE. Most of the ancient Persian empire is in modern-day Iran.

    pesticide Noun

    natural or manufactured substance used to kill organisms that threaten agriculture or are undesirable. Pesticides can be fungicides (which kill harmful fungi), insecticides (which kill harmful insects), herbicides (which kill harmful plants), or rodenticides (which kill harmful rodents.)

    petroleum Noun

    fossil fuel formed from the remains of ancient organisms. Also called crude oil.

    pharaoh Noun

    ruler of ancient Egypt.

    piranha Noun

    carnivorous, freshwater fish native to South America. Also called caribe.

    pirarucu Noun

    large freshwater fish native to the Amazon. Also called arapaima.

    plentiful Adjective

    abundant or full.

    pollution Noun

    introduction of harmful materials into the environment.

    Encyclopedic Entry: pollution
    precipitation Noun

    all forms in which water falls to Earth from the atmosphere.

    Encyclopedic Entry: precipitation
    prehistoric Adjective

    period of time that occurred before the invention of written records.

    protruding Adjective

    sticking out.

    Pschent Noun

    double crown worn by Egyptian pharaohs, symbolizing Upper and Lower Egypt.

    purify Verb

    to cleanse thoroughly.

    putrification Noun

    process of rotting or decaying.

    rain forest Noun

    area of tall evergreen trees and a high amount of rainfall.

    rapids Noun

    areas of fast-flowing water in a river or stream that is making a slight descent.

    Encyclopedic Entry: rapids
    recede Verb

    to go backward or withdraw.

    recreational Adjective

    having to do with activities done for enjoyment.

    replenish Verb

    to supply or refill.

    reservoir Noun

    natural or man-made lake.

    Encyclopedic Entry: reservoir
    restrict Verb

    to limit.

    river Noun

    large stream of flowing fresh water.

    Encyclopedic Entry: river
    river bed Noun

    material at the bottom of a river.

    river management Noun

    the art and science of controlling the flow, path, and power of rivers.

    river system Noun

    tributaries, mouth, source, delta, and flood plain of a river.

    rot Verb

    to decay or spoil.

    route Noun

    path or way.

    runoff Noun

    overflow of fluid from a farm or industrial factory.

    Encyclopedic Entry: runoff
    sailboat Noun

    aquatic vessel that uses wind to maneuver and move.

    Scandinavia Noun

    region and name for some countries in Northern Europe: Iceland, Norway, Sweden, Finland, and Denmark.

    seawater Noun

    salty water from an ocean or sea.

    sediment Noun

    solid material transported and deposited by water, ice, and wind.

    Encyclopedic Entry: sediment
    settlement Noun

    community or village.

    sewage Noun

    liquid and solid waste material from homes and businesses.

    sluggishly Adverb

    slowly.

    soil Noun

    top layer of the Earth's surface where plants can grow.

    source Noun

    beginning of a stream, river, or other flow of water.

    Encyclopedic Entry: source
    spring Noun

    small flow of water flowing naturally from an underground water source.

    stakeholder Noun

    person or organization that has an interest or investment in a place, situation or company.

    steamboat Noun

    boat powered by steam, used mostly on rivers. Also called a steamer.

    St. Lawrence Seaway Noun

    series of canals, locks, and channels, including the St. Lawrence River, that allows ships to travel from the Atlantic Ocean to the Great Lakes.

    stream Noun

    body of flowing fluid.

    sturgeon Noun

    type of marine or freshwater large, long, bony fish.

    subcontinent Noun

    large section of a continent.

    submerge Verb

    to put underwater.

    Tagaeri Noun

    people and culture native to the Amazon River basin in Ecuador.

    tectonic plate Noun

    large, moveable segment of the Earth's crust.

    temperature Noun

    degree of hotness or coldness measured by a thermometer with a numerical scale.

    Encyclopedic Entry: temperature
    textile Noun

    cloth or other woven fabric.

    Three Gorges Dam Noun

    electrical power plant along the Yangtze River in China.

    tide Noun

    rise and fall of the ocean's waters, caused by the gravitational pull of the moon and sun.

    Encyclopedic Entry: tide
    timber Noun

    wood in an unfinished form, either trees or logs.

    topsoil Noun

    the most valuable, upper layer of soil, where most nutrients are found.

    towboat Noun

    powerful boat used mostly on rivers to tow a line of barges roped behind it.

    toxic waste Noun

    chemical compound dangerous to humans and their environment.

    trade Noun

    buying, selling, or exchanging of goods and services.

    trading post Noun

    place established in a remote or unsettled region, where goods may be bought and sold.

    tribe Noun

    community made of one or several family groups sharing a common culture.

    tributary Noun

    stream that feeds, or flows, into a larger stream.

    Encyclopedic Entry: tributary
    tropical Adjective

    existing in the tropics, the latitudes between the Tropic of Cancer in the north and the Tropic of Capricorn in the south.

    typhoid Noun

    infectious, sometimes fatal disease that harms the intestines. Also called typhoid fever.

    Upper Nile Noun

    southern section of the Nile River.

    upstream Adjective

    toward an elevated part of a flow of fluid, or place where the fluid passed earlier.

    urban area Noun

    developed, densely populated area where most inhabitants have nonagricultural jobs.

    Encyclopedic Entry: urban area
    valley Noun

    depression in the Earth between hills.

    vapor Noun

    visible liquid suspended in the air, such as fog.

    vegetation Noun

    all the plant life of a specific place.

    virus Noun

    tiny organism that lives and multiplies in a living cell.

    water-borne Adjective

    transported or carried by water.

    water cycle Noun

    movement of water between atmosphere, land, and ocean.

    Encyclopedic Entry: water cycle
    waterfall Noun

    flow of water descending steeply over a cliff. Also called a cascade.

    Encyclopedic Entry: waterfall
    waterway Noun

    body of water that serves as a route for transportation.

    White Nile Noun

    tributary of the Nile River flowing from the highland rivers of Burundi to Lake Victoria and meeting the Blue Nile to form the Nile River at Khartoum, Sudan.

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