Lake Washington, a prominent feature near Seattle, Washington, often prompts a common question: is its water fresh or salty? This large body of water, central to the region’s geography and recreation, has a distinct hydrological identity. Understanding its water type and the factors maintaining it reveals an interplay of natural processes and human engineering.
A Clear Answer
Lake Washington is a freshwater lake. Despite its proximity to Puget Sound, a saltwater arm of the Pacific Ocean, the lake maintains a salinity level well below the threshold for freshwater. Measurements show salinity levels from 0.00 to 0.06 parts per thousand (ppt), well within the definition of freshwater (0.5 ppt or less). This status supports a diverse ecosystem and various human activities.
How Lake Washington Stays Freshwater
Lake Washington’s freshwater nature is maintained through natural inflows and an engineered system. The lake receives water from two major rivers: the Cedar River (57% of annual volume) and the Sammamish River (27%). Numerous smaller streams and rainfall also feed into the lake.
The lake’s outflow system directs water through Lake Union and via the Lake Washington Ship Canal to Puget Sound. The Hiram M. Chittenden Locks, also known as the Ballard Locks, are a key component. These locks maintain the water level of Lake Washington and Lake Union at 20 to 22 feet above sea level, above Puget Sound’s mean low tide.
The locks prevent saltwater from Puget Sound from mixing with the lakes’ freshwater. Saltwater, being denser, tends to sink. The locks employ a submerged barrier and a saltwater drain system; any saltwater that intrudes during vessel passages settles into a dredged basin and is then drained back into Puget Sound. This design ensures Lake Washington remains a freshwater body, even with constant boat traffic connecting it to the ocean.
Life and Activities in a Freshwater Lake
Lake Washington’s freshwater environment supports diverse aquatic life and recreational activities. The lake is home to numerous fish species, including salmon (Chinook, Coho, Kokanee), trout (rainbow, cutthroat), bass (largemouth, smallmouth), yellow perch, and black crappie.
The lake’s freshwater status makes it a popular destination for recreation. Swimming, boating, kayaking, and paddleboarding are common. Fishing is a year-round activity. Beyond recreation, Lake Washington plays a role in flood control and serves as a source of drinking water for some communities, drawing from the Cedar River.