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  1. Small lakes data and info
  2. Lake Information Page

Lake Information Page

Mirror Lake

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Vital Statistics

Watershed Area 166 acres
Lake surface area 18 acres
Maximum depth 27 feet
Mean depth feet
Public Park No
Boat Ramp No
Fish Present

Overview

Volunteer monitoring began at Mirror Lake in 1997 and continued through 2004, when it was discontinued. The data indicated that this city lake (Federal Way) is moderate in primary productivity (mesotrophic) with good water quality. Productivity appeared to be decreasing over time, the trend marked by a fairly high degree of statistical significance.

Profile data indicated that thermal stratification may be unstable through summer, and the sediments release little phosphorus into the deep water. Nitrogen to phosphorus ratios were above 20:1 through the summer, which generally favors other algae over bluegreens.

Mirror Lake has no public access points. However, residents should watch infestations of noxious weeds growing in the nearshore environment.

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Maps

bathymetric map
lake watershed map
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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For questions about lakes in King County, please contact lakes@kingcounty.gov or call the Water and Land Resources Division front desk at 206-477-4800.