The Johnstown Flood (locally, the Great Flood of 1889) occurred on May 31, 1889, after the catastrophic failure of the South Fork Dam on the Little Conemaugh River 14 miles (23 km) upstream of the town of Johnstown, Pennsylvania, USA. The dam broke after several days of extremely heavy rainfall, unleashing 20 million tons of water (18 million cubic meters) from the reservoir known as Lake Conemaugh.