King County logo
Lake Photo Image
Go to another lake:

Vital Statistics

Watershed Area 82 acres
Lake surface area 18 acres
Maximum depth 47 feet
Mean depth 23 feet
Public Park No
Boat Ramp No
Fish Present


Volunteers monitored Lake McDonald from 1996-2008 and resumed in 2014. This lake is moderate in color, lightly buffered against pH change, and since 1998 has decreased in primary productivity (eutrophic to mesotrophic), remaining steady since 2002. There may be a slow decrease in total nitrogen over time. Thermal stratification is stable through summer, but deep water phosphorus and ammonia data are not available for 2014. Nitrogen to phosphorus ratios in the upper water are generally above 25:1, which may not have given cyanobacteria a competitive advantage. A large bloom occurred in fall 2003, but was not tested for toxicity. No other events have been reported. Lake McDonald has no public access point, but residents should watch for early infestations of Eurasian milfoil or other noxious weeds.

Back to top


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

Back to top

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).

Back to top

Reports and Related Links

Back to top