Laurel Run Dam , also known as Laurel Run Dam No. 2 , was an earthen embankment dam that failed during the Johnstown Flood of 1977 . It had the largest reservoir of seven dams to fail between July 19 and 20 , 1977 and caused the most fatalities of the two that did . The dam failed in the early morning of July 20 after period of heavy rain , causing of water to flood downstream Tanneryville , killing 40 people
Johnstown Flood of 1977
Johnstown flood of 1977
Laurel Run Dam