The overall water quality of Walloon Lake is very good. The prospects for maintaining this level of quality are enhanced by the small watershed and by the marl in the water which buffers pollutants (phosphorus). However, the relatively long water residence time hampers the lake’s natural ability to cleanse itself. Phosphorus has been identified as the limiting nutrient in the lake. Phosphorus and nitrogen inputs to the lake must be minimized to maintain high water quality. The North Arm Basin has lower water quality than the other basins in Walloon Lake. The North Arm basin is more susceptible to eutrophication than the other basins in Walloon Lake because of its smaller volume and longer water residence time. Areas have been identified where shoreline soils do not adequately remove nutrients from septic system effluent. These areas constitute an appreciable source of pollution to Walloon Lake.