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 upstream of the town of
Johnstown, Pennsylvania. 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. With a volumetric flow rate that temporarily equalled that of the
Mississippi River, the flood killed 2,209 people and caused US$17 million of damage (about $450 million in 2015 dollars).