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Vital Statistics

Watershed Area 230 acres
Lake surface area 11 acres
Maximum depth 14 feet
Mean depth feet
Public Park N
Boat Ramp N
Fish Present


Volunteers monitored Allen Lake from 1994 – 2008 and resumed in 2014. The lake water is strongly colored, lightly buffered against pH change, and consistently high in primary productivity (eutrophic), with fair water quality. There was a persistent downward trend in productivity from 1996 to 2008 that was statistically strong, which appears to be continuing in 2014. Total nitrogen is also decreasing over time. Thermal stratification was stable in summer, and significant sedimentary phosphorus release increased deep water concentrations of phosphate. Nitrogen to phosphorus ratios were often at or below 25:1, which may favor cyanobacteria in the plankton. However, no toxins have been reported to-date. Allen Lake does not have a public access point. However, residents should watch aquatic plant populations to catch early infestations of Eurasian milfoil, Brazilian elodea, or other noxious aquatic weeds.

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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.
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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