Green-1 Lake

Vital Statistics
Overview
Maps
Water Quality Data
Reports and Related Links

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Continue to monitor nearshore plants to catch purple loosestrife and Brazilian elodea (Egeria densa). Both are regulated Class B noxious weeds that have been identified near Green Lake. If spotted, notify the King County Noxious Weeds Program.

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 2024 monitoring season are:

• In 2024, the TSI values were in the mesotrophic range. Mesotrophic lakes (TSI 40–50) have fairly clear water and moderate nutrient concentrations and algal growth. • Monitoring on Green Lake began in 2005, a year after an alum treatment. • Nitrogen-to-phosphorus (N:P) 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). • Long-term trends suggest that water quality in Green Lake has been declining over time, with increasing chlorophyll, nitrogen, and phosphorus concentrations. These trends are seen even with two alum treatments (2004 and 2016) since monitoring within the Lake Stewardship Monitoring Program began, in 2005. • An algal bloom was sampled for toxin testing in January. No algal toxins were detected in this sample.

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

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).

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.