<Tr> <Td> - Point of Rocks, MD </Td> <Td> 7,320 cu ft / s (207 m / s) </Td> </Tr> <Tr> <Td_colspan="2"> The Potomac River watershed covers the District of Columbia and parts of four states </Td> </Tr> <P> The Potomac River (/ pəˈtoʊmək / (listen)) is located along the mid-Atlantic Ocean coast of the United States and flows into the Chesapeake Bay . The river (main stem and North Branch) is approximately 405 miles (652 km) long, with a drainage area of about 14,700 square miles (38,000 km). In terms of area, this makes the Potomac River the fourth largest river along the Atlantic coast of the United States and the 21st largest in the United States . Over 5 million people live within the Potomac watershed . </P> <P> The river forms part of the borders between Maryland and Washington, D.C., on the left descending bank and West Virginia and Virginia on the river's right descending bank . The majority of the lower Potomac River is part of the State of Maryland . Exceptions include a small tidal portion within the District of Columbia, and the border with Virginia being delineated from "point to point" (thus various bays and shoreline indentations lie in Virginia). Except for a small portion of its headwaters in West Virginia, the North Branch Potomac River is considered part of Maryland to the low water mark on the opposite bank . The South Branch Potomac River lies completely within the state of West Virginia except for its headwaters, which lie in Virginia . </P>

Potomac river flows into what body of water