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Lake Eucha is first in a complex of two lakes. The second, Spavinaw Lake, is used as a water source by the City of Tulsa. Taste and odor problems made the water very expensive or impossible to treat in recent years. The source of these problems is thought to be algal blooms due to elevated nutrient concentrations in Lake Eucha. In a previous modeling study of the basin, we supported claims that the application of poultry manure was responsible for increased phosphorus load to Lake Eucha. We prepared a new model including more water quality and flow data, recent land cover data derived from Landsat TM+ imagery, high resolution (Next generation weather radar) NEXRAD precipitation data, and soil test phosphorus for both pastures and row crops. The Soil and Water Assessment Tool (SWAT) 2000 model was calibrated for flow at three gages and for phosphorus loads at eight locations. Phosphorus loads were estimated using the US Geologic Survey (USGS) program LOADEST2 using observed water quality measurements, and streamflow estimates provided by both the City of Tulsa and the USGS. The SWAT model predicts that the application of poultry litter and elevated soil test phosphorus in the basin is responsible for 49% of the current annual phosphorus load to the lakes.