A steady state lake phosphorus (P) mass balance model was used to predict the equilibrium P concentration (annual, volume-weighted average) of the lake water from natural and anthropogenic, external and internal P inputs. Internal P load was modeled as the product of sediment release rates and anoxic factors. Both these components were predicted from lake P concentration computed from external load to create a link between external and internal load components. Such estimates allow the modeling and setting of objectives of several hundred lakes on the Canadian Shield. In particular, estimates of predevelopment lake P concentration made by removing all anthropogenic inputs were compared with postdevelopment conditions in which additional loading was added to the model. This was accomplished by determining how much development would increase external as well as internal phosphorus load and ultimately annual average lake P concentrations. By comparing proposed lake development scenarios with existing or predevelopment scenarios, it can be determined whether water quality objectives will be exceeded.