Vollenweider Model examines phosphorus load and response characteristics for the relative general acceptability of the water for recreational use (Vollenweider, 1975). The model was developed by Vollenweider while working on the Organization for Economic Cooperation and Development (OECD) Eutrophication Study. Vollenweider found that when the annual phosphorus load to a lake is plotted as a function of the quotient of the mean depth and hydraulic residence time, lakes that were eutrophic tended to cluster in one area and oligotrophic lakes in another. Vollenweider developed a statistical relationship between areal annual phosphorus loading to a lake normalized by mean depth and hydraulic residence time, to predict lake phosphorus concentration. More information on the model can be found in: Vollenweider, R.A. 976, Advances in defining critical loading levels for phosphorus in lake eutrophication. Mem. Ist. Ital. Idrobiol., 33: 53-83.