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Vital Statistics

Watershed Area 185 acres
Lake surface area 31 acres
Maximum depth 15 feet
Mean depth 9 feet
Public Park Y
Boat Ramp Yes, no gas engines
Fish Present Bass, stocked rainbow


Volunteers monitored Lake Killarney from the late 1980s through 2008 and resumed in 2014. This lake, partly in Federal Way, has light water color and is poorly buffered against pH changes. It is fairly high in primary productivity (high mesotrophic to eutrophic) with fair to good water quality. There are no statistically significant trends since 1998. Thermal stratification is not stable through summer, and neither phosphorus nor ammonia build up in deep water. Nitrogen to phosphorus ratios are generally under 25:1, which can favor cyanobacteria, but no toxic events have been identified to-date.

Lake Killarney has a public boat launch and in the past has been heavily infested with milfoil. Though herbicide treatments were successful, residents should keep an eye on aquatic plants growing near shore to catch early new infestations.

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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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