As an alternative to loading graphs, a graph of mean influent phosphorus concentration versus phosphorus retention capacity is proposed to express the relationship between phosphorus supply and hydraulic flow to, and resultant trophic state of, lakes. Lines of constant lake phosphorus concentration drawn on the proposed graph delineate predicated trophic states and changes caused by altering influent phosphorus concentrations and/or lake phosphorus retention capacity. The graph, derived from the steady state solution of a phosphorus mass balance model, expresses lake mean phosphorus concentration as a function of mean influent phosphorus concentration and phosphorus retention capacity. Because the mean influent phosphorus concentration is a potential lake concentration reduced by the lake phosphorus retention capacity, a determination of the latter is critical for predicting lake phosphorus concentrations several empirical expressions are developed for oligtrophic lakes relating phosphorus retention capacity to areal hydraulic load or hydraulic washout coefficient. These expressions can be used to predict average lake phosphorus concentrations from mean influent concentrations.