The timber-crib dam was constructed in 1906 as a replacement for a similar 1901 dam and powerhouse on the same site. The dam is 39 feet (12 m) high and 257 feet (78 m) long at its crest,[2] placed into the narrows of Bear Trap Canyon. As one of eight PPL Montana hydro projects, it has a generating capacity of 9 megawatts (12,000 hp) in a run-of-the-river configuration.[3]Montana Power Company acquired the dam in 1912 as part of a merger, PPL Corporation purchased it in 1997 and sold it to NorthWestern Corporation in 2014.
The reservoir it creates, Ennis Lake, is 2.6 miles (4.2 km) long and has a maximum storage capacity of 42,053 acre-foot (51,872,000 m3).[2] The lake is relatively shallow and warms significantly during the summer, which tends to decrease fish populations.[4] The lake supports recreational fishing for brown trout and rainbow trout, camping, boating, and white-water rafting in Bear Trap Canyon downstream (north) of the dam.[5]
