ABSTRACTIn the 1975 National Eutrophication Survey Bear Lake had the best overall water quality of all Utah lakes sampled. However, this oligotrophic state would not be retained because of a mesotrophic level of loading. Because of the unique characteristics of the Bear Lake ecosystem and the present danger of cultural eutrophication, the objectives of this 314 Clean Lakes Study were to: (1) quantify the major nonpoint sources of nitrogen and phosphorus into Bear Lake; (2) quantify the major sources of nitrogen and phosphorus in the Bear River prior to its diversion into Dingle Marsh and Bear Lake; (3) determine the nitrogen, phosphorus, and carbon budgets of Dingle Marsh and define the factors which may regulate the flux of these nutrients into Bear Lake; and (4) if necessary, develop a set of viable cost-effective alternatives for the reduction of the nitrogen and phosphorus loading into Bear Lake. Nutrient loading was determined for each major tributary to Bear Lake and the trophic condition of the lake was determined over an 18-month period. Trophic state determinations were made using TSI values, areal oxygen deficits, and areal phosphorus loadings. Differences in parameters predictions are explained. An historical perspective of the water quality trends is given for Bear Lake (1975–1983). Based upon the observed changes and associated land use alterations, a series of management plans is proposed for maintaining or improving the water quality in Bear Lake.