History of the Dam and Plant

The Thompson Falls PPL Dam located in town on the Clark Fork River is a popular attraction for visitors. The Thompson Falls reservoir offers a variety of recreational opportunities including boating, fishing, swimming and floating.

Thompson Falls Dam has a seven-unit hydroelectric plant on the Clark Fork River in Thompson Falls. The units have a total generating capacity of 94 megawatts. (One megawatt can satisfy the average energy needs of 750 households.)

The Thompson Falls plant, which began operation in 1915, consists of a main dam and a dry-channel dam with an island in between. Both dams are used to regulate the reservoir, which has a storage capacity of 8,300 acre-feet, and control flow during high spring runoff. The main dam is 913 feet long and 32 feet high.

The dry-channel dam is a concrete gravity structure with an overflow spillway and an overall length of 289 feet. The structure has an average height of 17 feet above the riverbed. It is raised by flashboards and 8-foot drop panels. Thompson Falls is classified as a “run-of-river” project because it can generate electricity using the water that flows down the river, without the need to store additional water supplies.

The Clark Fork River at Thompson Falls was originally a natural waterfall.

Thompson Falls is one of two PPL Montana dams west of the Continental Divide. The Clark Fork River empties into the Columbia River, which in turn empties into the Pacific Ocean.