Muddy Run Pumped Storage Facility is a pumped-storage hydroelectric generation facility in Drumore Township, Pennsylvania, United States. Constructed by the Philadelphia Electric Company and completed in 1968, Muddy Run was the largest pumped-storage facility in the world. Muddy Run has a capacity of 1,071 megawatts. The facility is operated by the Susquehanna Electric Company, a subsidiary of Constellation Energy.