Silver Bow Creek is a headwater stream of the Clark Fork (river) originating within the city limits of Butte, Montana, from the confluence of Little Basin and Blacktail Creeks. A former northern tributary, Yankee Doodle Creek, no longer flows directly into Silver Bow Creek as it is now captured by the Berkeley Pit. Silver Bow Creek flows northwest and north through a high mountain valley, passing east of Anaconda, Montana, where it becomes the Clark Fork at the confluence with Warm Springs Creek. For more than one hundred years Silver Bow Creek was an open industrial sewer, primarily used as a depository for mining and smelting waste. A record flood in 1908 dispersed mass quantities of heavy metals and arsenic along its entire floodplain, which posed significant risks to environmental and human health. Superfund designation, remediation, and restoration The Upper Clark Fork river basin is America's largest Superfund site. Butte, at the headwaters, was the source of much of the watershed's contamination from over a century of industrial-scale mining and ore processing activities. This Superfund mega site includes the cities of Butte, Anaconda, Deer Lodge, and Bonner-Milltown (just upriver of Missoula). The contamination extends along a river corridor of that reaches from Butte to the Milltown Reservoir Superfund Site and includes adjacent areas such as the Anaconda Smelter Stack. The mining and smelting operations of the Anaconda Copper Mining Corporation were the primary cause of this pollution at the headwaters of the Clark Fork. The Anaconda Copper Mining Corporation (ACM) merged with the Atlantic Richfield Corporation (ARCO) in 1977. Shortly thereafter, in 1983, ARCO ceased mining and smelting operations in the Butte-Anaconda area. For more than a century, the ACM mined and smelted ore in Butte. Smelters operated in Butte until c. 1920 and in nearby Anaconda until 1981. In Butte, mine tailings and smelter waste were dumped directly into Silver Bow Creek, creating a plume of pollution extending down the valley to Milltown Dam on the Clark Fork just upstream of Missoula. Air- and waterborne pollution poisoned livestock and agricultural soils throughout the Deer Lodge Valley. Modern environmental clean-up efforts began under Superfund in 1983 and continue to this day. The Environmental Protection Agency (EPA) designated Silver Bow Creek as the Streamside Tailings (SST) Superfund site in 1985, with ARCO as the principal party responsible for remedy or clean-up. The EPA selected a remedy for the Silver Bow Creek