The structure was constructed in 1961-1964 by the United States Bureau of Reclamation, to hold water for downstream irrigation and for flood control purposes.

The reservoir has a total capacity of 325,324 acre-feet (401,281,000 m3), and when full has a surface area of 5,903 acres (23.89 km2).

Construction of the dam and reservoir required the relocation of U.S. Route 91 (rebuilt as Interstate 15) and a main line of the Union Pacific Railroad.

The reservoir inundated the former site of the small community of Armstead, Montana, and the site of Camp Fortunate, where the Lewis and Clark Expedition camped from August 17 to 22, 1805 and held negotiations with the Shoshone.

This Beaverhead County, Montana state location article is a stub.