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Vital Statistics

Watershed Area 160 acres
Lake surface area 15 acres
Maximum depth feet
Mean depth feet
Public Park N
Boat Ramp N
Fish Present

Overview

Volunteer monitoring began at Grass Lake in 2002 and continued through 2008, after which it was discontinued. The data suggested that this lake was moderately colored and high in primary productivity (eutrophic) with fair water quality. However, over the last few years the lake became so shallow during summer that the sample station could not be reached, so monitoring only occured in late spring through early summer.

Grass Lake has no public access boat ramp, but residents should monitor aquatic plants growing nearshore to catch early infestations of Eurasian watermilfoil, Brazilian elodea or other noxious aquatic weeds.

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Maps

Bathymetry map unavailable
This map shows the area of the watershed relative to the area of the lake. Generally speaking, the larger a watershed is relative to a lake, the greater the influence land use practices on lake water quality.

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



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