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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


The key takeaways from the 2018 monitoring season are:

• Green Lake continued to have fairly clear water, with moderate nutrient concentrations and algal growth. • Average 2018 phosphorus and chlorophyll concentrations, as well as Secchi depths, were noticeably higher than values observed in 2016 following the alum treatment in spring 2016. They were similar to values observed in 2013-2015, before the alum treatment. • Nitrogen-to-phosphorus (NP) ratios were below 25 throughout the monitoring season. This indicates the potential for algal blooms to be dominated by cyanobacteria (which have the ability to produce toxins). • An algal bloom was sampled for toxin testing in October. Toxin testing found low concentrations of algal toxins, well below the Washington State Recreational Guidelines.

Please see below for a link to the full 2018 Green Lake Monitoring Report.

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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

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

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