Potomac River

Potomac River. A major river in the Mid-Atlantic region of the U.S. that flows from the Potomac Highlands in West Virginia to the Chesapeake Bay in Maryland. It is 405 miles (652 km) long and is the fourth-largest river along the East Coast of the U.S. More than six million people live within its watershed.

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 right descending bank.

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.

All navigable parts of the river were designated as a National Recreation Trail in 2006.