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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


The key takeaways from the 2018 monitoring season are:

• Lake Dolloff continued to have fairly high nutrient concentrations and algal growth, and less-clear water. • Lake Dolloff's high nutrient concentrations and nitrogen-to-phosphorus (NP) ratios below 25 both indicate that Lake Dolloff is likely to have algal blooms dominated by cyanobacteria (which have the ability to produce toxins). • An algal bloom was sampled for toxin testing in early August. No algal toxins were detected in this sample.

Please see below for a link to the full 2018 Lake Dolloff 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 Dolloff Monitoring Report
2017 Lake Dolloff Monitoring Report

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