| Madison Dam | |
| Location Map: | Montana#USA |
| Coordinates: | 45.4701°N -111.6383°W |
| Country: | United States |
| Location: | Madison County, Montana |
| Purpose: | Hydroelectric, Flood Control, Water Supply, Recreation |
| Opening: | 1906 |
| Owner: | PPL MONTANA, LLC |
| Operator: | NorthWestern Corporation |
| Dam Type: | Timber crib |
| Dam Height: | 39feet |
| Dam Length: | 257feet |
| Res Name: | Ennis Lake |
| Res Capacity Total: | 42053acre-foot |
| Res Max Length: | 2.6miles |
| Res Elevation: | 1469m (4,820feet) |
| Plant Capacity: | 9 MW |
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 high and 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 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 long and has a maximum storage capacity of .[1] The lake is relatively shallow and warms significantly during the summer, which tends to decrease fish populations.[3] 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.[4]