A river’s source is the location from which it first flows. Sources include lakes, bogs, springs, streams, snow or precipitation accumulations, glaciers, wetlands, and other rivers.
Typically, rivers’ sources are located at greater elevations than their downstream portions. A tributary may also refer to a river or stream that flows into a larger river. Typically, the major stretch of a river flows through a floodplain en route to its mouth, where it empties its water into a bigger body, such as the ocean or a lake. The river’s source is the farthest point from the river’s mouth, also known as the estuary.