South Fork Dam was an earthen work dam on Lake Conemaugh ( formerly Western Reservoir , also known as the Old Reservoir and Three Mile Dam , a misnomer ) , an artificial body of water near South Fork , Pennsylvania , United States . On May 31 , 1889 , the South Fork Dam failed catastrophically and 20 million tons of water from Lake Conemaugh burst through and raced 14 miles ( 23 km ) downstream , causing the Johnstown Flood
Johnstown Flood
Johnstown Flood
South Fork Dam