Water Quality

March 9, 2025

Secchi Depth: 1.9 meters, (6.2 feet)
Water Temp: 8.5 C, (47.3 F)

Weekly water clarity and temperature data are posted on the King County Lakes website and available here (select Lake Green-1, From/To, and View Data). General lake information, water quality data, and reports are available here. Continuous water level and temperature gauge data are available here.

Learn how we monitor and treat the water.

Green Lake can experience algae blooms in late summer and fall that produce toxins and result in warnings of unsafe conditions for swimming.

The beaches are tested weekly during the summer for fecal coliform bacteria that very rarely result in beach closures.

For a current listing of Green Lake and other King County beach warnings to Stay Out Of The Water, go to the King County Lakes website here.

Lakes currently experiencing toxic algae blooms are also listed on the Washington State Toxic Algae website here.