Cameron Run is a 3.0-mile-long (4.8 km) tributary stream of the Potomac River, located in the U.S. state of Virginia. A third-order stream, it is formed by the confluence of Backlick Run and Holmes Run. It flows eastward from Alexandria and forms the border between Fairfax County and Alexandria before opening into Hunting Creek and then into the Potomac River. The lower course near Eisenhower Avenue is largely channelized and flows just north of the Capital Beltway until it crosses under it near Telegraph Road The lower 1 mile (1.6 km) or so is tidal and was navigable in colonial times. Cameron Run Regional Park, a water park, lies along a portion of the stream. Cameron Run is part of the Cameron Run Watershed, which encompasses a total of 44 square miles (110 km²) in Northern Virginia (33 square miles (85 km²) in Fairfax County).