The Helena Valley Unit is in central Montana, adjoining the city of Helena, Montana, and 3.5 miles west of Canyon Ferry Dam on the Missouri River. The principal purposes of the unit are irrigation and municipal water for the city of Helena. Features of the development are a tunnel, dam and regulating reservoir, canal, pumping plant, and other facilities. Created by Helena Valley Dam the reservoir, with 518 water surface acres, 477 land acres and 6 miles of shoreline, offers fair fishing for kokanee salmon. Picnic shelters available. Boating is non-motorized only.

Adjoins city of Helena, the capital city of Montana.