Lake Sawyer

Lake Sawyer is a freshwater lake in Black Diamond, Washington. Only three other natural lakes in King County have a larger surface area.

Lake Sawyer is underlain by glacial outwash and till dating from the Vashon Glaciation, as well as older glaciations that occurred during the Pleistocene. The bedrock underlying this mass of sediments is classified as the Hammer Bluff Formation, which was deposited during the Miocene epoch and consists of sedimentary rocks with some volcanic deposits. Discharge from the lake via groundwater outflow is thought to occur mostly in the northeast and southwest corners. Lake Sawyer is classified as mesotrophic, with algal growth limited by phosphorus availability. A 1994 survey found 23 species of plants growing in the lake and along its shorelines, including the invasive Myriophyllum spicatum and Nymphaea odorata.

A concrete dam was built at the outlet in 1952 to regulate the lake level. Several species of fish, some of which are stocked, can be caught in the lake.