"Everyone in the United States lives in a watershed. A watershed is a geographic area in which water flows on its way to a larger water body, such as a stream, river, estuary, lake, or ocean. The nationís coastal and ocean resources are affected not only by activities in coastal areas but also by those in upland watersheds. A coastal watershed, as defined by the National Oceanic and Atmospheric Administration, is that portion of a watershed that includes the upstream extent of tidal influence. In the Great Lakes region, a coastal watershed includes the entire geographic area that drains into one of the lakes."
The previous statement is quoted from chapter 9 of: