What is a river?
A river is a moving body of water that flows from its source on high ground, across land, and then into another body of water, which could be a lake, the sea, an ocean or even another river.
A river flows along a channel with banks on both sides and a bed at the bottom. If there is lots of rainfall, or snow or ice melting, rivers often rise over the top of their banks and begin to flow onto the floodplains at either side.
How are rivers formed?
Rivers usually begin in upland areas, when rain falls on high ground and begins to flow downhill. They always flow downhill because of gravity.
They then flow across the land - meandering - or going around objects such as hills or large rocks. They flow until they reach another body of water.
As rivers flow, they erode - or wear away - the land. Over a long period of time rivers create valleys, or gorges and canyons if the river is strong enough to erode rock. They take the sediment - bits of soil and rock - and carry it along with them.
Small rivers are usually known as streams, brooks or creeks. If they flow from underground they are called springs.