Rivers: Definition & Explanation

Instructor: Maria Howard

Maria is a teacher and a learning specialist and has master's degrees in literature and education.

Explore rivers and how they develop from small streams to swiftly flowing rapids. Learn about how rivers shape the land around them, creating canyons, flood plains and deltas.


A river is a large, flowing waterway. Rivers primarily carry freshwater, which is why people throughout history have made their homes by them. From the Nile River in northern Africa to the Thames flowing through London, rivers have provided people with drinking water, water for crops and easy ways to transport people and goods.

Throughout history, the Thames River in Great Britain has been an important resource for the humans and animals living near it.
Photo of the Thames River

How Rivers Begin

Rivers begin as humble trickles of water from lakes and springs or from melting snow and glaciers. Since they start in higher elevations, rivers can't help but travel downhill, taking in additional streams called tributaries along the way. The Amazon River, one of the longest in the world at over 6,259 kilometers (3,903 miles), is fed by over 1,000 tributaries.

Thanks to gravity, rivers grow in size and speed as they flow downhill. A current is the rate and strength of a river's movement. Rivers, of course, move more than just water. They also carry silt and other bits of earth called sediment. Along with a river's water, sediment shapes the land in its path. For millions and millions of years, the Colorado River has slowly shaped a section of the Rocky Mountains into a steep V-shaped valley called the Grand Canyon.

Humans build dams across rivers to store water in human-made lakes called reservoirs. Since reservoirs usually hold fresh water, that water can be put to farming and household use. There are a few bigger dams, including the Hoover Dam on the Colorado River, where the power of the water current is used to create electricity.

The Hoover Dam is one of many dams along the Colorado River. Water released from the reservoir has a current strong enough to generate electricity.
Photo of the Hoover Dam

Where Do Rivers Go?

Rivers continue their journey out of the mountains onto more gently-sloping land. Because this terrain is more easily eroded, rivers are able to carve out curved shapes called meanders. Sometimes a meander will be cut off from the rest of the river by sediment, creating a body of water referred to as an oxbow lake.

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