Mountain Lake Dam, situated in Olga, Washington, is a state-owned structure managed by the Washington Department of Ecology. Completed in 1905, this earth dam serves as a critical water supply source, with a maximum storage capacity of 3010 acre-feet and a normal storage of 2870 acre-feet. The dam stands at a hydraulic height of 17 feet and a structural height of 16 feet, providing essential water resources for the surrounding community.

This multi-arch dam on Cascade Creek in San Juan County not only fulfills its primary purpose of water supply but also caters to recreational activities in the area. With a surface area of 180 acres and a drainage area of 2.27 square miles, Mountain Lake Dam offers a picturesque setting for outdoor enthusiasts and water resource aficionados alike. Despite its high hazard potential, the dam has been deemed to be in satisfactory condition, as indicated by a recent inspection report in April 2019.

With its serene location and historical significance, Mountain Lake Dam stands as a testament to the enduring importance of water resource management in the face of climate challenges. As a vital infrastructure for water supply and recreation, this earth dam continues to play a crucial role in sustaining the ecosystem and meeting the needs of the local community in the beautiful landscapes of Washington State.