Hebgen Dam, Embankment dam in Gallatin County, Montana.

Hebgen Dam is a concrete-core earthen embankment dam on the Madison River in southwestern Montana, 85 feet (26 m) tall and 721 feet (220 m) long. It was built in 1914 to create Hebgen Lake, the reservoir it impounds. The dam stores and regulates water for downstream reservoirs and hydroelectric plants.

Built in 1914 by the Montana Power Company, Hebgen Dam was made to store and regulate water for downstream reservoirs and hydroelectric plants, not to generate power itself. The 1959 Hebgen Lake earthquake damaged it, sending water over the crest four times before repairs. PPL Corporation bought it in 1997 and sold it to NorthWestern Corporation in 2014.

The reservoir behind the dam, known as Hebgen Lake, is well known among fly fishing enthusiasts who come for its trout. In summer, the shoreline fills with campers and boaters who treat the area as a base for exploring the surrounding mountains.

The area around the lake is most accessible in summer, when roads and shoreline access are generally open and conditions are stable. Those planning to fish should check local regulations in advance, as the Madison River corridor has specific rules that apply to this stretch of water.

The 1959 magnitude 7.5 quake, centred 20 miles beneath the lake bed, was reported as the fourth largest ever recorded in the United States at the time. Water surged over the crest four times, and the dam was repaired within weeks. On 30 August 2008 two of its four hydraulic gates failed, releasing 3,400 cubic feet per second instead of the normal 900.