Improved assessment of flow, sediment, and nutrient losses from watersheds with computer simulation models is needed in order to identify and control nonpoint source pollution. One model, currently under consideration by the U.S. Environmental Protection Agency for watershed assessments, is the Soil Water and Assessment Tool (SWAT). In this report, the authors describe an application of SWAT for the Sny Magill Creek Watershed (SMCW), which covers 7,100 hectares in northeastern Iowa. The authors conclude that the SWAT model was generally able to predict flow, sediment, and nutrient losses. Additionally, the SWAT model provided useful insights about the importance of accurate data inputs, weaknesses in some of the data collecting methodologies, and the impacts of best management practices (BMPs) on water quality.