Please see also Headwater

The source of a river, usually a lake or a spring, is the farthest point of a river from its estuary or confluence with another river.

Where a river is fed by more than one source, it is usual to regard the highest as its source, the others being considered tributaries.

Near its source, a river is usually insignificant, being a mere stream or brook, growing as more and more water drains into it.