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.
Click image to enlarge
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).
