The Potomac River runs over 383 miles from Fairfax Stone, West Virginia to Point Lookout, Maryland. It affects more than 6 million people who live within the Potomac watershed, the 14,670-square-mile land area where water drains towards the mouth of the river. This map shows the location of the river and its watershed area which spans across several geological regions including the Appalachian Plateau, Ridge & Valleys, Blue Ridge, Piedmont, and Coastal Plain.
The main stem plus all major tributaries totals 12,878.8 miles making the Potomac River the 21st largest in the United States. The main tributaries of the Potomac River are North Branch, Savage River, South Branch, Cacapon, Shenandoah, Antietam Creek, Monocacy River, and Anacostia River. The Potomac empties into the Chesapeake Bay downstream.