Milltown Dam Collection, 1906-2007

The Milltown Dam was a hydroelectric dam located seven miles east of Missoula, Montana, at the confluence of the Clark Fork and Blackfoot rivers near Milltown and Bonner, Montana. William A. Clark, a renowned copper mine investor and U.S. Senator, built the dam in 1908, to power his sawmill located in the town of Bonner, Montana before its electrical services were extended to the surrounding communities. In 1929, Montana Power Company purchased the dam from Clark and operated it until 2003, when Northwestern Energy assumed ownership of the dam as part of a collective purchase of Montana Power Company's electric and gas network.

A few months after the dam was built, a flood washed toxic mine waste from the Anaconda Copper Mining Company's work site near Butte, Montana, 126 miles downstream before it settled in the newly formed reservoir behind the Milltown Dam. The severity of the toxic waste accumulation was not realized until 1981, when the Montana Department of Health and Environmental Science conducted its bi-annual water quality study that found high concentrations of arsenic in four residential wells in Milltown, Montana. This led to approximately 120 miles of the Clark Fork River being added to the Environmental Protection Agency's (EPA) National Priorities List (NPL), commonly referred to as a Superfund site, in September of 1983. The Milltown Dam was designated as one of three Operable Units (OU), a distinct area designated within a larger Superfund cleanup site, on the Clark Fork River. Over the next quarter of a century research and investigation into possible methods of containment, remediation, and restoration ensued as part of the most expensive Superfund cleanup operations in United States History at that time costing approximately $100 million.

Following the Milltown Dam's 1983 listing, local, state, and federal resources were focused on the containment of harmful mining waste until 1996, when a severe ice jam on the Blackfoot River scoured the reservoir's toxic sediments leading to increased public safety concerns. As a result, the EPA decided that the complete removal of the dam was the best plan of action. In 2006, contaminated sediments were moved to a disposal site in Opportunity, Montana, and the dam was removed in 2008.

Following the dam's removal, efforts to restore the watershed at the confluence of the Blackfoot and Clark Fork rivers began, and the area was designated as the 500-acre Milltown State Park. The park offers interpretive sites, historical information, and outdoor recreation opportunities. In addition to public access, efforts were made to restore native vegetation in the Clark Fork and Blackfoot river flood plains.