The Potomac River originates in the Allegheny Mountains of western Maryland, southern Pennsylvania, and West Virginia. It 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. The Upper Potomac is joined by the Cacapon, Shenandoah, and Conococheague Rivers on its way out of the mountains, with a watershed totaling 6,300 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, Interstate Commission on the Potomac River Basin, and U.S. Geological Survey.)
