The key takeaways from the 2023 monitoring season are:
• This year, Green Lake had less clear water, with high nutrient concentrations and moderate algal growth. • The increasing trends in chlorophyll, nitrogen, and phosphorus primarily reflect the timing of monitoring and alum treatments. Monitoring started in 2005, and the early years had low nutrient and chlorophyll concentrations due to an alum treatment in 2004. • Numerous algal bloom samples were collected for toxin testing in 2023. In August, October and December, toxin testing found elevated microcystin concentrations at 10.5, 13.9, and 11.6 µg/L respectively, above the Washington State Recreational Guideline of 8 µg/L. • Continue to monitor nearshore plants to catch purple loosestrife and Brazilian elodea (Egeria densa). Both are regulated Class B noxious weeds that has been identified near Green Lake. If spotted, notify the King County Noxious Weeds Program.
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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).
