Geography
What is a river?
Quick answer
A river is a large stream of fresh water that flows downhill from its source, often in hills or mountains, to its mouth at a sea, lake or another river.
In one sentence
A river is a natural channel of fresh water that flows downhill until it reaches a sea, a lake or a bigger river.
Explained
Rivers are a big part of the water cycle. Rain and melting snow fall on high ground, and gravity pulls the water downhill. Small streams join up and grow into a river.
Every river has a source (where it starts) and a mouth (where it ends). Smaller rivers that join it are called tributaries, and the place where two rivers meet is a confluence. All the land that drains into one river is its river basin.
Rivers change along the way. Near the source, the upper course, the river is usually narrow, fast and steep, cutting V-shaped valleys and sometimes forming waterfalls. In the middle and lower course, the land is flatter, the river is wider and slower, and it swings in big loops called meanders. Near the mouth, a river may drop the mud it carries and build a fan of land called a delta, or widen into a funnel where it meets the tide, called an estuary.
Which river is longest? Most books say the Nile (about 6,650 km), with the Amazon (about 6,400 km) close behind. But the answer depends on where you decide each river begins, and some measurements make the Amazon longer. What nobody disputes is that the Amazon carries more water than any other river.
Examples
| River | Where | Something to know |
|---|---|---|
| Nile | Africa | flows north into the Mediterranean Sea |
| Amazon | South America | carries the most water of any river |
| Niger | West Africa | joined by the Benue in Nigeria; ends in the Niger Delta |
| Ganges | India and Bangladesh | forms one of the world's largest deltas |
| Thames | England | flows through London to an estuary |
| Mississippi | United States | ends in a large delta in the Gulf of Mexico |
Common mistakes
- Thinking rivers flow south. Rivers flow downhill in any direction. The Nile flows north.
- Mixing up source and mouth. The source is the start; the mouth is the end, like a river "speaking" into the sea.
- Saying rivers are salty. River water is fresh. It becomes salty only where it mixes with the sea.
Quick quiz
Rivers
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Question 1 of 4
What is the source of a river?
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