The public used to be able to walk across the top of Holter Dam ( which provided easy access to both sides of the river ) , but the dam was closed to the public after the September 11 attacks . Holter Dam was one of the last two such PPL dams to be closed . In 2014 , PPL sold Holter Dam and their other Montana dams to NorthWestern Corporation
September 11 attacks
September 11 attacks
Holter Dam