Lake Assessment Program - Circle Lake, Rice County

Circle Lake was sampled during the summer of 1991 as part of the Minnesota Pollution Control Agency's (MPCA) Lake Assessment Program. Data collected during the study showed that in terms of total phosphorus, chlorophyll and Secchi disk transparency, the water quality of Circle Lake is poorer than similar lakes in the same ecoregion. The mean summer concentrations of total phosphorus and chlorophyll were 575 and 126 ug/1 (ug/1 = micrograms per liter) respectively and the mean Secchi disk transparency was 4.1 feet. Based on these values, and on Carlson's Trophic Status Index (TS!) (Carlson, 1977), which ranges from O (very oligotrophic) to 100 (hypereutrophic), Circle Lake would be considered hypereutrophic. The average TS! value for Circle Lake is 78.