In the 1940s, miners used metals-laced tailings to build the Mike Horse Dam at the origins of the Blackfoot River on Beartrap Creek near the Continental Divide. In 1975, the tailings dam blew out, dumping deadly levels of lead, copper and zinc into the Blackfoot. The mine’s corporate owner, ASARCO, rebuilt the dam soon after, but the safety of the shored-up dam was always in question. Its base was constructed with 2 million cubic yards of toxic tailings that leaked polluted water. Furthermore, the dam’s spillway was not up to standards. The structure was at risk of overtopping in a large flood. Spurred by the threat of another catastrophic flood contaminating the river, the Clark Fork Coalition developed an outreach campaign that generated 8,000 public comments to the U.S. Forest Service urging removal of the dam and cleanup of mine waste.

From 2010 to 2021, the dam was dismantled and the mine tailings moved to a high and dry location. Now, the headwaters of the Blackfoot River are finally on the way to fully healing.