The Bureau of Reclamation is preparing a comprehensive plan for water resource development of the entire Umatilla Basin. In developing the proposed plan for construction of dams, canals, and other facilities, they have considered all water needs, such as irrigation, municipal and industrial water supplies, fisheries and recreation. The purpose of this investigation was to predict the water quality resulting from project development and to recommend steps to improve water quality where it will not meet requirements. A dissolved oxygen model was developed for the main stem Umatilla River from Ryan Reservoir to the mouth. Predictions of dissolved oxygen levels were prepared for the time horizons of 1980, 2000, and 2020. Conditions with and without the project were modeled.