Nestled between Auburn and Bonney Lake, Lake Tapps is a recreationist’s dream at 15 miles wide and with 4.5 miles of surface area on which one can canoe, jet ski, fish, paddle board, or enjoy Fourth of July fireworks from a pontoon party boat. The 45 miles of shoreline predominantly abut private waterfront homes with a few public-access points scattered around its perimeter. 

But what many may not know is that it also is a possible future source of Eastside drinking water.

Owned by the Cascade Water Alliance — a municipal corporation that retains not only the water, but the lakebed and the shoreline between the water and the 545-foot elevation line — Lake Tapps basically is a backup plan. 

The Cascade Water Alliance is made up of five cities: Bellevue, Redmond, Kirkland, Issaquah, and Tukwila — and the sewer and water districts of the Sammamish Plateau and Skyway. It was formed in April 1999 when the rapidly growing Eastside cities were faced with the possibility that Seattle’s water supply could not accommodate their growth in perpetuity. This had a lot of Eastsiders concerned over their future, according to Cascade’s intergovernmental and communications director, Elaine Kraft.

Cascade looked at several options across the Eastside and into the South Sound, eventually alighting on Lake Tapps. In 2009, it purchased the White River–Lake Tapps Reservoir Project from Puget Sound Energy. 

“Everything that is done on Lake Tapps is done with an eventual eye for municipal water supply,” Kraft said. 

Lake Tapps was formed from four smaller lakes, which include Lake Kirtley, Lake Crawford, Church Lake, and Lake Tapps. Prior to Cascade’s acquisition, the lake was used for hydroelectric power — “Tapps” is an acronym that stands for Tacoma and Puget Power Systems. 

In 1911, Puget Sound Power and Light — the predecessor of what we know today as Puget Sound Energy, or PSE — constructed a series of dikes into the existing landscape of forests and farms around the four lakes. A series of dams were then built, and a 12-mile flume diverted Mount Rainier meltwater from the White River to fill the massive reservoir. 

Water from the Lake Tapps reservoir would then flow through underground pipes down to a powerhouse on East Valley Highway between Auburn and Sumner and through giant turbines to generate hydroelectric power before it would once again rejoin the White River. 

This process continued until 2004, when PSE halted all power production on the White River–Lake Tapps project due to licensing disputes with the Federal Energy Regulatory Commission.

Today, one of Cascade’s priorities to ensure healthy water is working closely with the residents of Lake Tapps to ensure best practices are observed in yard care, septic maintenance, dock construction, and recreation. 

After all, fertilizer run-off from residents’ yards combined with the warmer water temperatures associated with global warming could lead to toxic algae blooms like those found in the reservoir in 2016. Additionally, roadway run-off, animal waste run-off from nearby farms, and pollution from watercraft threaten the reservoir. 

It is for this reason that Cascade’s draw-down of the reservoir for municipal water still is a long way off. According to the organization’s website, it is projecting a 2030 start for the project. It also stipulates that the project “requires construction of a treatment facility and additional transmission pipelines.”