• Lake McDonald has fairly clear water with moderate nutrient concentrations and moderate algal growth.
• Long-term trends suggest that water quality in Lake McDonald has been improving over time, with decreasing nitrogen and chlorophyll concentrations.
• Chlorophyll concentrations in 1996-2000 were substantially higher than those observed from 2001 onwards. This trend is not described in the table above, since the estimates for the amount and percent of change assume a constant, linear trend -- but the chlorophyll trend is distinctly non-linear.
• Nitrogen-to-phosphorus (N:P) ratios were above 25 for most of the monitoring season. This indicates a low likelihood for the algal community to be dominated by cyanobacteria (which have the ability to produce toxins).
• No algal blooms were reported for toxin testing in 2024.
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.
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).
