Under conditions of anoxia, lake sediments will liberate sorbed phosphorus compounds into the overlying water. The magnitude of the sediment-liberated phosphorus load will be a function of the concentration of phosphorus in the sediments, the area of lake bottom overlayed by anoxic water, and the temporal duration of anoxic conditions. In some cases the resulting phosphorus load may be a substantial component of the lake's annual phosphorus budget. This may have serious implications in the restoration and management of such lakes. The importance of internally-generated phosphorus loads in the nutrient budget of New Jersey's two largest lakes, Lake Hopatcong and Greenwood Lake, was assessed. The formation and depth of the thermocline were established from temperature profiles. The volume of the hypolimnion and the area of lake bottom overlayed by the hypolimnion were calculated. Following stratification, water column profiles of total phosphorus and dissolved oxygen concentrations were monitored. These data were used to compute the internally generated phosphorus load. In both lakes, a 10-fold increase in the concentration of total phosphorus was observed following the depletion of oxygen in the hypolimnion. The internally generated load associated with this phenomenon represents 5.9 percent and 29.3 percent of the annual total phosphorus budget of Lake Hopatcong and Greenwood Lake, respectively. The relevance of endogenous phosphorus loading is discussed for each lake in relation to its existing trophic status and future restoration and management.