Potomac

River of the eastern USA, forming the boundaries between West Virginia, Virginia, and Maryland states. Rising in the Allegheny Mountains, it flows 459 km/285 mi southeast into Chesapeake Bay. It is created by the confluence of the North Potomac, 153 km/95 mi long, and South Potomac, 209 km/130 mi long, and its chief tributaries are the Shenandoah and the Monocacy. At Washington, DC, 185 km/116 mi from its mouth, the Potomac becomes tidal and navigable for large ships.

Historic sites such as Mount Vernon, the home of George Washington, are situated along its banks. Potomac appeared on the Most Endangered Rivers list in 1998 because of pollution caused by local poultry and cattle industries. An environmental pressure group, Potomac Conservancy, was established in 1993.