A gun on USS ''Princeton'' explodes while the boat is on a Potomac River cruise, killing eight people, including two United States Cabinet members.

The territory of the District of Columbia south of the Potomac River (39 mi² or about 100 km²) is returned to Virginia through an Act of Congress.

American Civil War: the Potomac River is crossed at White's Ford in the Maryland Campaign.

Mayor of Tokyo Yukio Ozaki presents Washington, D.C. with 2,000 cherry trees, which President Taft decides to plant near the Potomac River.

Shortly after takeoff, Air Florida Flight 90, a Boeing 737 jet crashes into Washington, DC's 14th Street Bridge and falls into the Potomac River, killing 78 including four motorists. Coincidentally, 30 minutes later, a Washington Metrorail train derails at the Federal Triangle station, on the orange and blue lines, killing three and injuring many more. Flight 90 also destroyed part of a Blue line track that ran next to the 14th street bridge. This gridlocked the city.