Madison Dam

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Madison Dam
Madison River near Ennis January 2015 14.JPG
Madison Dam, January 2015
LocationMadison County, Montana
Coordinates45°28′12″N 111°38′18″W / 45.47012°N 111.63831°W / 45.47012; -111.63831Coordinates: 45°28′12″N 111°38′18″W / 45.47012°N 111.63831°W / 45.47012; -111.63831
PurposeHydroelectric, Flood Control, Water Supply, Recreation
Operator(s)NorthWestern Corporation
Dam and spillways
Type of damTimber Crib
Spillway capacity7700 cfs
Total capacity42053 ac.ft.

Madison Dam is a hydroelectric dam on the Madison River in Madison County, Montana, in the southwestern part of the state.

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,[1] 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.[2] 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.[3] 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]