The Potomac River is the second-largest tributary of the Chesapeake Bay, after the Susquehanna River, flowing 380 miles past Washington, D.C. to meet the Chesapeake Bay near Point Lookout, Maryland. Downstream of the nation’s capital is the tidal, oligohaline Lower Potomac, which drains an area of 1,800 square miles. The entire Potomac watershed, including the Shenandoah River, is 14,670 square miles. More than half of this watershed is forested, while another quarter is agricultural and about 14% is developed land. (Based on American Rivers, the Interstate Commission on the Potomac River Basin, and the U.S. Geological Survey.)
