Great Falls Park, Nature reserve in Fairfax County, United States

Great Falls Park is a nature reserve in Fairfax County containing roughly 800 acres where the Potomac River flows through steep rock formations. The river creates natural waterfalls and carves through the Mather Gorge, a dramatic canyon formed by exposed rock layers.

The Patowmack Canal within the park dates to the early American period when engineers attempted to make the Potomac navigable for commerce. This canal system reflects the historical importance of water transportation for connecting communities and moving goods.

The park's name comes from the Great Falls of the Potomac, which drop 76 feet over a series of cascades. The Patowmack Canal ruins and the vanished town of Matildaville lie along the trails, and stonemason marks on the lock stones match those on White House and U.S. Capitol foundation stones.

Enter by car via Georgetown Pike (Route 193) or Old Dominion Drive; the park opens only during daylight and the lot for 600 vehicles can fill by early morning on busy weekends, causing closures of several hours. Fifteen miles of trails follow Difficult Run, and a riverside path climbs from the stream's mouth to the top of Mather Gorge. Camping is not permitted, and entering the water above the falls from the Virginia side is illegal.

The park draws over 150 bird species throughout the year, many of which find shelter in the rocky terrain and riverside vegetation. Wildlife like whitetail deer, foxes, and coyotes also roam the grounds, often visible to attentive visitors exploring the trails.