The project objective was to develop methodology for evaluating and predicting the impact which various parameters and components of waste water have on the dynamic oxygen balance in a receiving water. Dynamic oxygen balances obtained under a variety of oxygenation and deoxygenation conditions were studies in the laboratory using batch reactors and in the field using natural streams. The Streeter-Phelps expression for the mathematical description of oxygen sag curves was found inaccurate due to inclusion of the first order expression for describing substrate utilization by bacteria. Monod Equations were found valid for defining bacterial substrate utilization and protozoa bacterial utilization. Substrate utilization as determined by the COD test was found to be dependent on the time frame for sampling. It was found that the shorter the time frame, the greater the variances and apparent inconsistencies in the data. Techniques were developed for determining Monod Equation constants using batch reactor data and data obtained under continuous dilution in a natural stream. In general, the studies indicate that laboratory evaluation of the impact of alternative methods of water resources management on the oxygen resources of the receiving stream is valid. (WRSIC abstract)