watershed

The entire region draining into a river, river system, or other body of water.

A ridge of high land dividing two areas that are drained by different river systems.

A critical point that marks a division or a change of course; a turning point.

The area drained by a river and all its tributaries.

The edge of a river-basin (see river); the line separating the waters flowing into two different rivers or river-basins.

The whole region or extent of country which contributes to the supply of a river or lake.

The line of division between two adjacent rivers or lakes with respect to the flow of water by natural channels into them; the natural boundary of a basin; — called also divide and water parting.

a point in time marking an important transition between two situations, or phases of an activity; a turning point.

The topographical boundary dividing two adjacent catchment basins, such as a ridge or a crest.

A region of land within which water flows down into a specified body, such as a river, lake, sea, or ocean; a drainage basin.