Proposed and existing pulp mill developments in the Athabasca River Basin impact on winter dissolved oxygen conditions in the rivers that receive their effluent. In 1987, Alberta Environment started using water quality models to simulate dissolved oxygen levels. This information was used to formulate effluent standards and for management of basin water quality. This report describes the theory of air to liquid gas exchange, methods to measure reaeration, the procedure designed to measure under ice reaeration, results of the field study, and conclusions from the study