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Vital Statistics

Watershed Area 1875 acres
Lake surface area 259 acres
Maximum depth 30 feet
Mean depth 13 feet
Public Park Yes
Boat Ramp car top boats
Fish Present bass, carp, stocked RB trout


Water quality monitoring began at two stations at Green Lake in 2005 and continued through 2008. Green-2, which was discontinued in 2009, is located in the southwest section of the lake, offshore from the boating center. Data suggest that this city lake (Seattle) is nearly colorfree and currently moderate in primary productivity (mesotrophic), with good water quality. Not enough data are available to assess trends since the alum treatment in 2004. Profile data indicate that thermal stratification is not stable through summer, and nutrients are mixed through the water column. Nitrogen to phosphorus ratios are commonly below 20:1, which may favor bluegreens over other algae.

Green Lake is surrounded by a heavily used city park. The lake was treated with aluminum sulfate in 2004 to reduce internal phosphorus loading to control toxic bluegreen algae blooms. There are established infestations of Eurasian milfoil, and water lily that have been the targets of past control activities.

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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

Friends of Green Lake
Green Lake Hydrologic Data

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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.