The worst flood in United States history happened in Johnstown, Pennsylvania, on May 31, 1889.
The town is situated on the South Fork of the Little Conemaugh River. The South Fork Dam, some 15 miles (24 kilometers) north of Johnstown, had been built in 1853, but fell into disrepair.
The lake created by the dam was stocked with fish so that vacationers along its banks could enjoy fishing on their holidays. Wire screens were installed in front of the lake’s outlets to prevent the fish from escaping.
The screens became completely clogged with silt and aquatic plant growth, so that when heavy rains fell the night of May 30, 1889, the water had no natural release.
The pressure of the mounting water broke the dam at 3 o’clock on May 31. A wall of water reaching 20 to 30 feet (6 to 9 meters) in the air rushed at a speed of 22 feet (7 meters) per second toward Johnstown.
Within a matter of minutes, the town was flooded and most of its inhabitants were either dead or left homeless.