Second only to the Susquehanna River in size and output, the Potomac River serves as the southern headwaters for the Chesapeake Bay. The tidal portion of this river covers approximately 50 miles from Washington, D.C. to the mouth of the river at the Maryland-Virginia border. The river is home to many species of fish and offers many opportunities for recreation to the residents of the U.S. capital. (Based on American Rivers.)