The Clark Fork River, located in southwestern Montana, is a tributary of the Columbia River in the northwestern United States. The Upper Clark Fork River area is known for its cold-water trout fishing. The Upper Clark Fork River from the Butte and Anaconda area to the Milltown Reservoir is contaminated with several heavy metals primarily from historical mining activities. The Silver Bow Creek, the Upper Clark Fork River, and Milltown Reservoir have been designated as Superfund sites by the U.S. Environmental Protection Area. Scientific studies indicate that the trout in these areas are at high risk from elevated metal concentrations due to their contaminated diet.