Interstate 90 Floating Bridges

Lake Washington () is a large freshwater lake adjacent to the city of Seattle, Washington, United States.
It is the largest lake in King County and the second largest natural lake in the state of Washington, after Lake Chelan. It borders the cities of Seattle on the west, Bellevue and Kirkland on the east, Renton on the south, and Kenmore on the north, and encloses Mercer Island. The lake is fed by the Sammamish River at its north end and the Cedar River at its south.

Lake Washington has been known to the Duwamish and other Indigenous peoples living on the lake for millennia as (lit. "lake" in Lushootseed). At the time of European settlement, it was recorded as At-sar-kal in a map sketched by engineer Abiel W. Tinkham; and the Chinook Jargon name, ("great/large water"), was also used. Other English names historically used for the lake include Lake Geneva by Isaac N. Ebey; and Lake Duwamish in railroad surveys under Governor Isaac Stevens. Lake Washington received its present name in 1854 after Thomas Mercer suggested it be named after George Washington, as the new Washington Territory had been named the year before.

The lake provides boating and sport fishing opportunities. Some fish species found in its waters include sockeye salmon, coho salmon, Chinook salmon, rainbow trout, largemouth bass, smallmouth bass, yellow perch, and black crappie.

Lake Washington has two passenger seaplane bases: Kenmore Air Harbor on its north end; and Will Rogers – Wiley Post Memorial Seaplane Base on its south end, adjacent to Renton Municipal Airport.

Geography

Lake Washington's basin was formed by glacial processes associated with the Puget lobe of the Cordilleran Ice Sheet during the Vashon Glaciation, likely through a combination of preferential erosion of weak rock and sediments by the glacier itself and by subglacial meltwater during the glacier's retreat. At the end of the Pleistocene, the basin that is now Lake Washington connected directly to the channels of Puget Sound through the north end of the Duwamish Valley. The basin may or may not have been a waterway at this point, as eustatic sea levels were approximately lower than at present and the land around Seattle was about lower due to isostatic depression from the weight of the glacier. However, the rapid sea level rise from the end of the Pleistocene through the early Holocene had flooded the Duwamish Valley and Lake Washington within a couple thousand years. Lake Washington did not become a freshwater lake, isolated from Puget Sound, until some time after 5,700 years Before Present, when sedimentation in the Duwamish Valley closed off its southern end. The new lake, lacking any other outlets, drained south through the Black River into the Duwamish Valley and, ultimately, Puget Sound until the construction of the Lake Washington Ship Canal in 1916.

Creeks and rivers

The main inflowing rivers are the Sammamish and Cedar Rivers, with the Cedar supplying most of the water. Seasonal changes in the flow of the Sammamish are moderated by a weir at the Lake Sammamish inlet.

The lake is drained by the Lake Washington Ship Canal.

In addition, there are numerous small creeks and rivers which feed the lake, including:

* Coal Creek
* Denny Creek ( O.O. Denny Park)
* Fairweather Creek
* Forbes Creek
* Juanita Creek
* Kelsey Creek
* Little Creek
* Lyon Creek
* Mapes Creek
* May Creek
* McAleer Creek
* Mercer Slough
* Ravenna Creek
* Taylor Creek
* Thornton Creek
* Yarrow Creek
* Yesler Creek

Historically, construction of the Lake Washington Ship Canal drastically changed the inflow and outflow of the lake. Before construction of the canal in 1916, Lake Washington's outlet was the Black River, which joined the Duwamish River