River

A river is, by definition:"'A natural stream of water of fairly large size flowing in a definite course or channel or series of diverging and converging channels.' (dictionary.com)"Rivers are joined by tributaries (usually, but not exclusively, smaller rivers), or can themselves join a larger river as a tributary. A river begins at its source and ends at its mouth, which may be an estuary, if the river flows all the way to the sea, or may be a confluence with another river. A system of rivers makes up a drainage basin.