Chisago Lakes Chain of Lakes Watershed TMDL

The Clean Water Act (1972) requires that each State develop a plan to identify and restore any waterbody that is deemed impaired by state regulations. A Total Maximum Daily Load Study (TMDL) is required by the Environmental Protection Agency (EPA) as a result of the federal Clean Water Act. A TMDL identifies the pollutant that is causing the impairment and how much of that pollutant can enter the water body and still meet water quality standards. In the case of the Chisago Lakes Chain of Lakes Watershed, the lake impairment affects the lake's ability to support aquatic recreation (which includes: fishing, swimming, boating, and aesthetics). The impairment is caused by excessive nutrients in the lakes; the nutrient found to be causing the main problem is phosphorus. Phosphorus is a necessary nutrient in lake ecology; however, too much phosphorus can cause excessive algae blooms. These algae blooms can sometimes be toxic and have unpleasant odors. Nine lakes within the Chisago Lakes Chain of Lakes Watershed are currently on the EPA's 303(d) Impaired Waters List (or Draft list): North Center, South Center, Wallmark, Little, Ogren, Linn, Pioneer, School, and Emily (see Table 10 for impairment listing). This TMDL report will address the impairments, provide an assessment of the ecological health of each lake, assess potential phosphorus sources, and provide guidelines on how to restore the aquatic recreational use of each lake.