The Chesapeake Bay watershed spans six states and the District of Columbia. Within this watershed are several large cities, including Cooperstown, N.Y.; Harrisburg, Pa.; Baltimore, Md.; Washington, D.C.; and Norfolk, Richmond and Charlottesville, Va.

Altogether, more than 100,000 streams, creeks and rivers thread through the Chesapeake Bay watershed.

A subwatershed is a small watershed contained within the larger Chesapeake Bay watershed. Each of the streams, creeks and rivers in the Bay watershed has its own watershed. For example, the Potomac River watershed is a subwatershed of the Chesapeake Bay watershed.