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Vital Statistics

Watershed Area 1037 acres
Lake surface area 62 acres
Maximum depth 54 feet
Mean depth 21 feet
Public Park Y
Boat Ramp Yes, no gas engines
Fish Present bass, stocked rainbow


Volunteers monitored the main basin of Beaver Lake in Sammamish from the 1980s-2014.The lake water is moderately colored, lightly buffered against pH change, and mid-range in primary productivity (mesotrophic), with good water quality that has been stable since 1998. Sensitivity of the lake to development is discussed in the Beaver Lake Management Plan (see links). Thermal stratification remains stable in summer, and sediments release some phosphorus to deep water, where ammonia build-up signals low oxygen. Nitrogen to phosphorus ratios are regularly below 25:1, which can favor cyanobacteria. Beaver-2 was monitored for cyanotoxins in 2009-2011, but levels have remained very low. Beaver-2 has a public boat ramp and a popular park with beach access. A multi-year project testing for E.coli bacteria found the water was safe for recreational activities.

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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

Beaver Lake Management Plans

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