It was created in 1983 by Puget Sound Energy and operated for hydroelectric power until it ceased power production in 2004. In December 2009 Puget Sound Energy (PSE) sold the lake to the Cascade Water Alliance, a municipal corporation whose members are five cities (Bellevue, Issaquah, Kirkland, Redmond, and Tukwila) and two water districts (Sammamish Plateau Water and Sewer District, and the Skyway Water and Sewer District). Cascade provides water to almost 350,000 residents and more than 20,000 businesses. It plans to eventually use Lake Tapps as a municipal water supply source.