Swimming Use Support of Minnesota Lakes. Fully Supporting - Few algal blooms and adequately high transparency exist to support swimming throughout the summer. (Corresponds to Carlson's TSI values below 51 for NLF, 53 for NCHF, and 57 for WCP and NGP ecoregions)
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Fully Supporting (marginal) - Swimmable use is still fully supported, but the lake is near the P limit for its ecoregion and small increases in in-lake P could result in increased algal blooms and perceptible decreases in transparency. (Corresponds to Carlson's TSI values between 51 - 53 for NLF, 53 - 57 for NCHF and 57 - 65 for WCP and NGP ecoregions)
Partial Supporting (impaired) - Algal blooms and low transparency may limit swimming for a significant portion of the summer. (Corresponds to Carlson's TSI values between 53 - 61 for NLF, 57 - 63 for NCHF and 65 - 69 for WCP and NGP ecoregions)
Non Supporting - Severe and frequent algal blooms and low transparency will limit swimming for most of the summer. (Corresponds to Carlson's TSI values above 61 for NLP, 63 for NCHF and 69 for WCP and NGP ecoregions)
Minnesota Lake Water Clarity
Estimated From Early 1990’s Landsat Satellite Images
Research funded by:
TSI(SDT) Carlson’s trophic state index as calculated from Secchi disk transparency( SDT) a measure of water transparency.
TSI <30 Classic Oligotrophy; Clear water, oxygen through the year in the hypolimnion, salmonid fisheries in deep lakes.TSI 30-40 Deeper lakes still exhibit classical oligotraphy, but some shallower lakes will become anoxic in the hypolimnion during the summer.TSI 40-50 Water moderately clear, but increasing probability of anoxia in hypolimnion during summer.TSI 50-60 Lower boundary of classical eutrophy: Decreased transparency, anoxic hypolimnion during the summer, macrophyte problems evident, warm-water fisheries only.TSI 60-70 Dominance of blue-green algae, algal scums probable, extensive macrophyte problems.TSI 70-80 Heavy algal blooms possible throughout the summer, dense macrophyte beds, but extent limited by light penetration. Often would be classified as hypereutrophic.TSI > 80 Algal scums, summer fish kills, few macrophytes, dominance of rough fish.
Adapted from www.pca.state.mn.us/water/lakeacro.html
Average Water Clarity By Ecoregion
Average Lake TSI(SDT)/Average Acre TSI(SDT)/# Lakes Assessed
Leif Olmanson, Marvin Bauer and Patrick Brezonik
Water Resources Center and Remote Sensing Laboratory
University of Minnesota