The 1889 Johnstown Flood was caused by the failure of the South Fork Dam , part of the Main Line of Public Works . The dam across the Little Conemaugh River in the hills above Johnstown , Pennsylvania , created a two-square-mile ( 5.2 km2 ) reservoir . Dubbed Lake Conemaugh , it supplied water to the Western Division Canal . When canal traffic declined , the lake and dam were abandoned , then sold to the Pennsylvania Railroad in 1857 ; the railroad in turn sold them to private interests . They were purchased by the South Fork Fishing and Hunting Club in 1879 , and a private resort was built surrounding the lake . On May 31 , 1889 , following heavy rains , the South Fork Dam failed , sending 20 million tons ( 18.2 million cubic meters ) of water down the gorge toward Johnstown . More than 2,200 people were killed
Johnstown Flood
Johnstown Flood
Main Line of Public Works