In order to tackle the eutrophication of Lake Erie, USA and Canada agreed to reduce phosphorus levels by 40% by 2025. An accurate simulation of water quality and quantity is essential to achieve this goal. Although widely used and well documented, the Soil and Water Assessment Tool (SWAT) uses a single nationwide US curve to derive channel geometry parameters, and a simplistic mass-balance approach simulates sediment and nutrients in water bodies. This study tested the applicability of regional regression equations for in-stream and reservoir processes. Their impact on water quantity and quality was investigated for two Canadian watersheds- Guelph and Pittock reservoirs. Results showed that using watershed and reservoir characteristics is essential to produce realistic and accurate hydrologic simulations. Finally, the regression equations used in the study produced better results than the SWAT routine for water quality simulation.