The Chatfield Watershed Authority requested a modeling solution that would aid in tracking sources of phosphorus from the watershed and allow for the evaluation of management decisions. Lynker teamed with an experienced engineering firm to complete the project which included a thorough model selection process, data collection of hydrologic and water quality data, data gap analysis, and building and calibrating a HSPF water quality model. The model was built to track total phosphorus loading to Chatfield Reservoir so that best management practices could be implemented to reduce total phosphorus concentrations. Model development included the collection of model input data (precipitation, potential evapotranspiration, wind speed, land use, soils data, etc.), watershed delineation, as well as point source loading data. The hydrologic component of the model was calibrated using USGS streamflow data, while the water quality processes were calibrated using grab sample data provided by the Chatfield Watershed Authority. The model is used to connect with the Chatfield Reservoir model to complete management scenario analyses in the future.