High Quality Content by WIKIPEDIA articles! The Occoquan River is a tributary of the Potomac River in northern Virginia, in the mid-Atlantic region of the United States. The river is 24.7 miles (39.8 km) long, and its watershed covers about 590 square miles (1,528 km2). It is formed by the confluence of Broad Run and Cedar Run in Prince William County; Bull Run enters it east-southeast of Manassas, as the Occoquan turns to the southeast. It reaches the Potomac at Belmont Bay. The Occoquan River is part of the Chesapeake Bay watershed. The name Occoquan is derived from a Doeg Algonquian word translated as "at the end of the water".