The relative susceptibility of lakes in the Alpine Lakes Wilderness Area to water-quality degradation was evaluated from two perspectives: (1) water-quality sensitivity, which is the tendency of a lake 's water quality to degrade in response to pollutant loading, and (2) pollutant-loading likelihood, which is determined by the presence of drainage-basin features that enhance the transport of pollutants to a lake. Water-quality sensitivity was evaluated for 60 lakes, using a mass-balance phosphorus model to predict the response of each lake to a hypothetical ' worst-case ' increase in phosphorus loading. This evaluation suggested that lakes in the Alpine Lakes Wilderness Area generally are not sensitive to foreseeable increases in phosphorus loading because of their high rate of dilution and flushing. Pollutant-loading likelihood was evaluated according to the amount of seasonal ' wet area ' near a lake and in the drainage basin. Of 298 lakes evaluated for pollutant-loading likelihood, 74 lakes were rated moderate to high. On the basis of these findings, lakes in the Alpine Lakes Wilderness Area are generally not considered susceptible to long-term degradation as a result of recreational use, but some lakes are probably susceptible to temporary local pollution. The nature of this potential problem, and knowledge of natural features of the Alpine Lakes Wilderness Area, suggest an approach for managing recreation so that the risk of water-quality degradation is minimized. (USGS)
