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Avoid all areas of algae accumulation along the shoreline; they could contain toxins harmful to people and pets.

Vital Statistics

Watershed Area 1875 acres
Lake surface area 259 acres
Maximum depth 30 feet
Mean depth 13 feet
Public Park Yes
Boat Ramp No, car top boats OK
Fish Present bass, carp, stocked RB trout

Overview

The key takeaways from the 2019 monitoring season are:

• Green Lake has fairly clear water, with moderate nutrient concentrations and high algal growth. • Average 2019 chlorophyll, nitrogen, and phosphorus concentrations were noticeable higher than values observed in 2018. These concentrations are also noticeably higher than values observed before the alum treatment that occurred in spring 2016. • Algal blooms in June-July and again in October-November resulted in Algal Toxin Warnings. Toxin testing found elevated microcystin concentrations above the Washington State Recreational Guideline of 6 µg/L.

Please see below for a link to the full 2019 Green Lake Monitoring Report.

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Maps

This bathymetric map shows contour lines of equal depth, similar to a topographic map would for mountains and valleys. The red 'X' marks the location where water quality samples are taken.
Watershed map unavailable

Click image to enlarge

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Water Quality Data  

Through a combination of efforts by volunteer lake monitors and King County staff, data relating to physical, chemical, and biological aspects of the lake have been collected for most lakes. The King County Lake Stewardship Program analyzes data to track long-term water quality trends in small lakes in western King County.

View or Download Data
Use this tool to view or download data from the lake in tabular format. You can define date ranges and select which parameters to view or download.

Chart Data
Use the charting tool to look at graphs showing single parameters for a single water year at a time.

Water quality over time
A common method of tracking water quality trends in lakes is by calculating the “trophic state index” (TSI) (Carlson, 1977) and testing the values for positive or negative trends over time. TSI indicators predict the biological productivity of the lake based on water clarity (Secchi) and concentrations of total phosphorus (TP) and chlorophyll a (Chlor). Generally at least 8 years of data without major lake management activities are needed to have confidence in a significant trend.

The average of these three TSI indicators during the growing season can be used to place lakes in one of three broad categories:
<40 = oligotrophic (low productivity),
40 to 50 = mesotrophic (moderate productivity)
>50 = eutrophic (highly productive).

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Reports and Related Links

2019 Green Lake Monitoring Report
2018 Green Lake Monitoring Report
2017 Green Lake Monitoring Report
Friends of Green Lake

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For questions about lakes in King County, please contact lakes@kingcounty.gov or call the Water and Land Resources Division front desk at 206-477-4800.