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Lake Sawyer is the fourth largest natural lake in King County with a surface area of 286.1 acres. The lake is located two miles northwest of Black Diamond and lies within the Big Soos Creek Basin of the Green River Watershed. The lake is used extensively for boating, water skiing, swimming and fishing. Public access is provided at the King County Lake Sawyer Park on the northwest side of the lake, and the newly acquired County Park in the southern part of the lake. The City of Black Diamond annexed the lake and surrounding homes in 1998. The City of Black Diamond is on the verge of significant expansion and growth which could have significant impacts on the water quality of Lake Sawyer.

Lake Sawyer has had historical water quality problems related to the discharge of wastewater from a failed wetland treatment system. The wastewater was diverted to the sanitary sewer in 1992. A draft lake management plan was developed in 1996 by King County to address the long-term water quality protection of the lake and watershed. The City and County have been conducting additional stormwater monitoring in the watershed to better identify sources of phosphorus to the lake.

Lake Sawyer, Black Diamond, WA
Lake Sawyer

The management approach for Lake Sawyer and its watershed as stated in the Draft Management Plan is to address the nutrient loading from the watershed to maintain its existing conditions. In-lake treatments such as alum and/or hypolimnetic aeration, are recommended as contingency measures in the event that monitoring results reveal that watershed controls are insufficient.

Lake Sawyer has been part of the Lake Stewardship Volunteer Monitoring Program since 1994. Twice a month from May through September, volunteers collect total phosphorus, chlorophyll a, total nitrogen, and phytoplankton samples to send to the County lab. Additional measurements, such as temperature, Secchi depth, precipitation, and lake level are collected by volunteers weekly throughout the year.

Lake Sawyer Recreation

Lake Sawyer and watershed data

Lake Sawyer drainage area and park location map

Lake Sawyer Watershed - Black Diamond area

Lake Sawyer bathymetric contour map

Lake Sawyer bathymetry map - small

For more information about Lake Sawyer, contact the City of Black Diamond at 253-631-0351.

For questions about Lake Sawyer and other small lakes in King County, please contact Rachael Gravon, Water Quality Planner or Chris Knutson, Project Manager, Lake Stewardship Program.