The 525-foot-high Yellowtail Dam impounds the Bighorn River at Fort Smith, Montana. Yellowtail Dam was completed in 1965 and changed a good warmwater fishery into a high quality tailwater trout fishery below the dam. Its construction created and made accessible Bighorn Lake which lies in a sand- and limestone-walled defile cut between the Bighorn and Pryor Mountains by the Bighorn River. Hundreds of feet down, within the Bighorn Canyon, water is backed up some 41 miles in Montana and 30 miles into Wyoming. In Montana, Bighorn Lake has a surface area of 5574 acres. Yellowtail Dam is used for peaking power with the Yellowtail Afterbay Dam 2 miles downstream functioning as a re-regulating facility. Because of the dam, streamflow in the river is relatively stable with little daily fluctuation. Bighorn Lake, like the river reach it inundated, supports a warmwater fishery.