The Potomac River is a major river in the Mid-Atlantic region of the United States that flows from the Potomac Highlands in West Virginia to the Chesapeake Bay in Maryland. It is 405 miles long, with a drainage area of 14,700 square miles, and is the fourth-largest river along the East Coast of the United States and the 21st-largest in the United States. More than 5 million people live within its watershed.