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.
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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).