Lake Sawyer, lake in Washington, United States of America

Lake Sawyer is a natural freshwater lake in Black Diamond, Washington, with three islands and a surface area exceeded by only three other natural lakes in King County. It lies over glacial outwash and till from the Vashon Glaciation and older Pleistocene glaciations, on bedrock of the Miocene Hammer Bluff Formation. A concrete dam built at the outlet in 1952 regulates its level.

Lake Sawyer is a natural freshwater lake formed in glacial outwash and till from the Vashon Glaciation and older Pleistocene glaciations, over bedrock of the Miocene Hammer Bluff Formation. A concrete dam built at its outlet in 1952 regulates the lake level; the lake itself was not created for water storage.

The area is easy to access with parking around the lake that allows visitors to reach the water quickly. Trails along the shore enable walking and biking, with fishing requiring a license and boats subject to safety rules.

A 1994 survey recorded 23 plant species in and along the lake, among them the invasive Eurasian watermilfoil (Myriophyllum spicatum) and the fragrant water lily (Nymphaea odorata). The lake is mesotrophic, and algal growth is limited by phosphorus availability. Groundwater outflow is thought to leave mainly at the northeast and southwest corners.