Lake Assessment Program - Long Lake and Horseshoe Lake, St Louis County

Long and Horseshoe Lakes were sampled during the summer of 1992 as part of the Minnesota Pollution Control Agency's (MPCA) Lake Assessment Program. Data collected during the study period showed that in terms of total phosphorus, chlorophyll and Secchi disk transparency, the water quality of Long and Horseshoe Lake is comparable to or slightly lower than minimally impacted (reference) lakes in the ecoregion. Mean summer concentrations are as follows: total phosphorus 31 ug/1 and 32 ug/1, chlorophyll 14.1 ug/1 and 15.1 ug/1 and mean Secchi disk transparency were 2.7 and 2.2 meters respectively. Based on these water quality values Long and Horseshoe Lake would be considered mesotrophic to slightly eutrophic. Phosphorus, chlorophyll and transparency measurements correspond quite well for each lake. This means that Secchi disk transparency can provide. good estimates of phosphorus and chlorophyll and can be a useful tool for tracking future trends. Based on Carlson's Trophic Status index (Carlson 1977) Long and Horseshoe Lake would be considered borderline eutrophic.