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.

[3] At the time of European settlement, it was recorded as At-sar-kal in a map sketched by engineer Abiel W. Tinkham;[4]: 10  and the Chinook Jargon name, Hyas Chuck ("great/large water"), was also used.

[9] 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.

A Washington State Department of Transportation (WSDOT) investigation revealed that the incident resulted from the improper handling of hydrodemolition water being used during the renovation, rather than in any basic flaw in the bridge's concept or design.

Concrete floating bridges continue to remain a viable means for the conveyance of vehicle traffic over Lake Washington.

[14] In 1950, approximately one year after the tolls were removed from the Murrow bridge, the inland ferry system on the lake came to an end, having operated since the 1880s.

During the 1940s and 1950s, eleven sewage treatment plants were sending state-of-the-art treated water into the lake at a rate of 20 million gallons per day.

The lake responded to the massive input of nutrients by developing unpleasant blooms of noxious blue-green algae (cyanobacteria).

The water lost its clarity, the desirable fish populations declined, and masses of dead algae accumulated on the shores of the lake.

Citizen concern led to the creation of a system that diverted the treatment-plant effluents into nearby Puget Sound, where tidal flushing would mix them with open-ocean water.