Rattlesnake Wilderness Dams

by Rob Roberts, TU National

Big Lake

The City of Missoula acquired ten dams on eight mountain lakes in the Rattlesnake Wilderness Area during the 2017 acquisition of the Mountain Water Company. The dams were originally built in the 1920s as part of the Rattlesnake Creek water supply, which along with the former lower Rattlesnake Creek dam, formed the community’s water supply. Currently, the wilderness dams have not been used for water delivery in more than 30 years, suffer from a lengthy maintenance backlog and are largely nonoperational. Overall, the City does not have the staff or financial resources to repair and maintain the suite of 10 dams and strategic decisions need to be made to alleviate inspection requirements, operation and financial obligations.

Sanders Lake

With recent successful removal and restoration of the lower Rattlesnake Dam in 2020 by the City, TU, and Montana FWP, partners are looking for more opportunities to improve fisheries, water quality and water quantity through management of the wilderness lakes and the Upper Rattlesnake Creek system. Rattlesnake Creek is a high priority fisheries area for Montana FWP because it is considered a stronghold for native fish like westslope cutthroat, bull trout and mountain whitefish. For more than two decades, Montana FWP, Montana TU, the WestSlope Chapter of TU and partners have attempted to conserve, protect and improve fisheries in Rattlesnake Creek through research projects, habitat improvement and fish passage projects such as screening irrigation ditches and habitat improvement.

McKinley Lake

In 2018, The City’s water utility – Missoula Water - completed an engineering evaluation of the wilderness dams, with preliminary recommendations to potentially repair the dams with the largest water rights for long term water storage and decommission the other dams with smaller water rights. The preliminary plan includes a pilot dam decommissioning project at McKinley Lake and continued data collection and assessment to evaluate the cost/benefit of rehabilitation options at Sanders Lake, Big Lake and potentially others. Sanders Lake and Big Lake have a combined water right total of approximately 60% of the storage volume (nearly 25 cfs) in the Rattlesnake Wilderness lakes, and since late summer is often the most stressful time for fish and other aquatics, the possibility of releasing cold water stored in these lakes could be a huge boost to Rattlesnake Creek. A pilot dam decommissioning project at McKinley Lake could happen as early as 2022, while the evaluation of Sanders and Big Lake will be ongoing. The City and TU plan to have solicit public input and feedback about the general goals and visions for projects sometime in the spring of 2021.