Watch The Johnstown Flood for Free: How to Stream the Movie Online at 123Movies. . On May 30, 1889 the South Fork Dam, which maintained a pleasure lake for wealthy Pittsburgh industrialists and their families, failed due to very heavy rains and poor maintenance by the dam's owners. The burst dam sent a wall of water and debris, 40 feet high and half a mile wide, 14 miles downstream to the bustling industrial city of Johnstown, Pennsylvania. More than 2000 people lost their lives in the disaster. This documentary tells the story, and tells us that the disaster was easily avoidable.