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Vital Statistics

Watershed Area 960 acres
Lake surface area 51 acres
Maximum depth 50 feet
Mean depth 23 feet
Public Park No
Boat Ramp No
Fish Present NA


The key takeaways from the 2018 monitoring season are:

• Lake Retreat had two distinct phases in 2018. Before mid-August, it had very clear water with low algal growth. After mid-August, it had moderately clear water and moderate algal growth. • Lake Retreat had fairly low phosphorus concentrations, but fairly high nitrogen concentrations. • Long-term trends suggest that water quality in Lake Retreat has been declining over time, with increasing nitrogen and phosphorus concentrations, and shallower Secchi depths. • No algal blooms were reported for toxin testing in 2018.

Please see below for a link to the full 2018 Lake Retreat Monitoring Report.

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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

2018 Lake Retreat Monitoring Report
2017 Lake Retreat Monitoring Report

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