Phosphorus loading from precipitation and more than a dozen tributaries of Big Beat Lake, Woman, was determined for the period from January to December 1978. Direct precipitation contributed 1120 kg·P·yr-1 (0.096 g P·m-2·yr-1) while tributary runoff contributed 21,560 kg for a total P loading of 1.84 g P·m-2 Rathbone creek, although accounting for only 4 percent of the hydro-logic input to Big Bear Lake, contributed \>27 percent of the annual phosphorus load. Phosphorus loading increased with increased impervious geology and increased development. Nitrogen loading exhibited similar loading patterns. Big Beat Lake is currently eutrophic and is likely to remain eutrophic. Calculations based on Vollenweider’s critical phosphorus loading concept indicated that tributary P-loading would have to be reduced by \>95 percent to achieve mesotrophic conditions. The completion of Big Bear Dam created a “naturally” eutrophic re mix which dl require proper management to enhance its resource potential.