A river basin is the area that drains into a river. Every drop of water that falls as rain makes its way to rivers.

Some rivers basins are gigantic. Nearly two thirds of the land of the USA drains into the Mississippi River, for example. Almost the whole of Brazil, and parts of several other countries, drains into the Amazon River. (Find out more about these in our books on the Mississippi and Amazon).

River Basins consist of a main 'trunk' river and many branches, or tributaries that bring water from every part of the basin. Most basins are 'leaf-shaped' or 'teardrop' shaped, with the end of the river being at the stem of the leaf or the neck of the teardrop. But some basins are very long and thin. The Nile is like this because it travels through a desert. Find out about the Nile and the Colorado in our separate books.