There are so many rivers on Earth. Small rivers and streams do merge and form larger ones. They carry their waters to the seas and oceans. Other rivers, such as the Volga, flow into the inland seas and lakes. And some become smaller and smaller until they disappear altogether or evaporate.


The rivers receive their water from precipitation as well as from melting snow and glaciers on mountain tops, from springs or mountain lakes. Large rivers have many tributaries (smaller rivers flowing into them).


Even giant rivers such as Ohio and Missouri are actually just tributaries of the even more full-flowing river Mississippi. Each of them, in turn, feeds from smaller tributaries, so that the vast Mississippi river system consists of thousands of rivers and streams. A river basin is a piece of land which feed a particular river system


Rivers irrigate the soil, but they also destroy it by washing out year after year and carrying it into the ocean. This process is very slow, but in thousands years the results are very noticeable. The Grand Canyon is formed by the American Colorado River and is a clear example of the destructive effect of the river even for the rocks.