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Water quality grades are based on standards established by the Metropolitan Council. The standards give a range to each letter grade for the May through September averages of surface total phosphorus concentration, surface chlorophyll a concentration, and Secchi depth. The overall lake water quality grade is the average of the grades for each parameter. Other indicators of lake condition such as aquatic plant growth or invasive species are not factored into these grades. The TSI, which measures the productivity level of a lake or degree of eutrophication, is also calculated. High TSI values correspond with poorer water quality.

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