Type of dam Timber Crib Total capacity 42053 ac.ft. | Spillway capacity 7700 cfs Owner PPL MONTANA LLC | |
 | ||
Location Madison County, Montana Purpose Hydroelectric, Flood Control, Water Supply, Recreation Operator(s) NorthWestern Corporation Similar Bear Trap Canyon National, Hebgen Dam, Morony Dam, Toston Dam, Canyon Ferry Dam | ||
Madison Dam is a hydroelectric dam in Madison County, Montana, in the southwestern part of the state.
Map of Madison Dam, Ennis, MT 59729, USA
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 high and 257 feet long at its crest, placed into the narrows of Bear Trap Canyon. As one of eight PPL Montana hydro projects, it has a generating capacity of nine megawatts in a run-of-the-river configuration. 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 long and has a maximum storage capacity of 42,053 acre-feet. The lake is relatively shallow and warms significantly during the summer, which tends to decrease fish populations. The lake still support recreational fishing for brown trout and rainbow trout, camping, boating, and white-water rafting in Bear Trap Canyon downstream (north) of the dam.