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Vital Statistics

Watershed Area 411 acres
Lake surface area 41 acres
Maximum depth 28 feet
Mean depth feet
Public Park No
Boat Ramp Yes, no gas engines
Fish Present bass, stocked rainbow


Volunteers monitored Lake Twelve from the early 1980s- 2004 and resumed in 2014. The lake water is clear, moderately buffered against pH change, and low to moderate in primary productivity (low mesotrophic) with good water quality. It appears to have remained fairly stable since it was last monitored in 2004. Recent trends cannot be evaluated because of the large data gap. Thermal stratification may be somewhat unstable in summer, and nutrients in the deep water do not appear to be enhanced by sediment release. Nitrogen to phosphorus ratios are generally above 25:1, which does not favor cyanobacteria. There are no toxic events identified to-date. Lake Twelve has a public access boat launch. An infestation of Eurasian milfoil was treated in the 1990s, but has since reappeared. Residents should keep an eye on this, as well as watch for other noxious weeds such as Brazilian elodea.

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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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