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Brazilian elodea has established a large population in the lake. Check boat trailers, fishing tackle, and boats carefully to ensure you don't transport Brazilian elodea to other lakes!

Vital Statistics

Watershed Area 580 acres
Lake surface area 22 acres
Maximum depth 31 feet
Mean depth 13 feet
Public Park Yes
Boat Ramp Yes
Fish Present rainbow trout, grass carp

Overview

Volunteers monitored Lake Fenwick in 1994 -1995, 2001, 2003-2004 and again beginning in 2021.

The key takeaways from the 2023 monitoring season are:

• Lake Fenwick continued to have fairly clear water, high algal growth, and high nutrient concentrations. • An algal bloom was sampled for toxin testing in October. Toxin testing found very low concentrations of algal toxins, well below the Washington State Recreational Guidelines. • Lake Fenwick has an infestation of Brazilian elodea (Egeria densa), a class B Noxious Weed, however because it is widely established around the lake, there is no requirement to control.

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Maps

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

Lake Stewardship Program: 2023 Monitoring Update
Lake Stewardship Program: 2022 Monitoring Update
2021 Lake Fenwick Monitoring Report

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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.