“A watershed is the land area that drains to a single body of water such as a stream, lake, wetland, or estuary. Hills or ridgelines often bound watersheds; interior valleys collect precipitation in streams, rivers, and wetlands.

These physical boundaries define the movement of water and delineate the watershed. Watersheds are nested - larger watersheds like the Chesapeake Bay encompass many smaller watersheds.”

Protecting and Restoring America’s Watersheds. EPA, June 2001