WIKI: Canyon Ferry Lake is a reservoir on the Missouri River near Helena, Montana and Townsend, Montana. It is Montana's third largest body of water, covering 35,181 acres and 76 miles of shore . It was formed by the building of Canyon Ferry Dam, which was completed in 1954 and has been used for electricity, irrigation, and flood controls since. The lake is a popular outdoor destination providing boating, fishing, wildlife habitat, and is nestled against the Big Belt Mountains