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Vital Statistics

Watershed Area 518 acres
Lake surface area 20 acres
Maximum depth 19 feet
Mean depth feet
Public Park N
Boat Ramp Y, no gas engines
Fish Present stocked rainbow, bass


Volunteer monitoring began at Lake Dolloff before 1985 and continued through 2001; some data were collected in 2008, after which it was discontinued. The data classified this lake as strongly colored and high in primary productivity (eutrophic) with fair water quality.

Profile information indicated that thermal stratification was relatively stable through summer, and the sediments released some phosphorus into the deep water. Nitrogen to phosphorus ratios were generally above 20:1 through the summer, which often favored other algae over bluegreens.

Lake Dolloff has a public access boat ramp, and Brazilian elodea was identified in 2004. Early infestation treatment was not successful, and it has continued to increase. Eurasian watermilfoil has also been identified in the lake, but does not appear to be increasing over time.

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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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