One of the many lock & dam combos along the C & O Canal near the Great Falls of the Potomac River (pic at right; click to enlarge).

The C&O Canal follows the route of the Potomac River for 184.5 miles from Washington, D.C. to Cumberland, MD.  The canal operated from 1828-1924 as a transportation route, primarily hauling coal from western Maryland to the port of Georgetown in Washington, D.C.

The C&O has become one of D.C.'s great green spaces—a narrow but quiet, beautiful, and relatively smooth (for biking, running, or walking) park that runs for miles and miles. In an area where 28 to 43 square miles of green space disappear every day, something like the C&O is a godsend.