[3] The lake, with a mean elevation of 13 feet (4 m) above sea level,[2] empties into the Siltcoos River, which meanders generally west for about 3 miles (4.8 km) to its mouth on the Pacific Ocean.

The lake formed after melting glaciers caused a rise in sea level that drowned the lower reaches of Oregon's coastal rivers.

[1] The shallowness contributes to the lake's eutrophic nature, related to extensive populations of Elodea, Myriophyllum, and other aquatic plants.

For 52 days in the fall of 2007, state and local authorities advised against domestic use of the lake water because of a dense bloom of Anabaena planktonica, a blue-green algal species that can produce toxins.

The Oregon Department of Environmental Quality (DEQ) has placed the lake on its list of impaired water bodies because of its problems with algae.