This study seeks to identify factors controlling dissolved oxygen (DO) concentrations in the Athabasca River. The work has three components: field measurement, laboratory study and computer modeling. The field study was conducted in the Athabasca River during the winter of 2004. Sediment oxygen demand (SOD) values were obtained under ice using a closed chamber method; oxygen microsensors were fabricated to both determine the oxygen dynamics at the sediment/water interface and its potential use as an alternative to in situ SOD incubations. The USEPA Water Analysis Simulation Program (WASP6) was chosen as the predictive tool for modeling. The model was calibrated using data from extreme low-flow, low DO years (2002 to 2003) and field and laboratory quantification of SOD. This study provided insight into the role of SOD in northern rivers, and improved the accuracy of dissolved oxygen modeling.