South Fork Dam

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The South Fork Dam was located on Lake Conemaugh, an artificial body of water located near South Fork, Pennsylvania. On May 31, 1889, the South Fork Dam failed and 20 million tons of water from Lake Conemaugh burst through and raced 14 miles (23 km) downstream, causing the Johnstown Flood.

The South Fork Dam was originally built between 1838-1853 by the State of Pennsylvania as part of the canal system to be used as a reservoir for the canal basin in Johnstown. It was abandoned by the state, sold to the Pennsylvania Railroad, and sold again to private interests.

Speculators had purchased the abandoned reservoir, made less than well-engineered repairs to the old dam, raised the lake level, built cottages and a clubhouse, and created the South Fork Fishing and Hunting Club. Members of the exclusive and secretive retreat in the mountains were 61 wealthy Pittsburgh steel and coal industrialists, bankers and lawyers including Andrew Carnegie, Andrew Mellon, Philander Knox and Henry Clay Frick.

Lake Conemaugh at the club's site was 450 feet (137 m) in elevation above Johnstown. Stocked with fish, the lake was about two miles (3 km) long, approximately one mile (1.6 km) wide, and 60 feet (18 m) deep near the dam. The lake had a perimeter of 7 miles (10 km) to hold 20 million tons of water. When the water was "up" in the spring, the lake covered over 400 acres (1.6 km²).

The dam was 72 feet (22 m) high and 931 feet (284 m) long. Between 1881 when the club was opened, and 1889, the dam frequently sprung leaks and was patched, mostly with mud and straw. Passersby sometimes commented about the likelihood of a failure, but no action was taken. The flawed dam held the waters of Lake Conemaugh back until May 31, 1889.

After several days of unprecedented rainfall, the dam gave way. A torrent of water raced downstream, destroying several towns. When it reached Johnstown, 2,209 people were killed, and there was $17 million in damage.