In the experimental part, the objective was to correlate rapidly determined parameters (i.e. chemical oxygen demand, organic carbon and ammonia) with 5-day BOD using linear regression analysis on samples taken from the Passaic River in New Jersey. Equations were developed for the prediction of the 5-day BOD -20C- (dilution technique), the 5-day 20C BOD (Warburg technique), and the 20-day 20C BOD (Warburgtechnique) from the ammonia, organic carbon, and chemical oxygen demand concentrations. The resulting equations indicated that only somewhere between 40% and 80% of BOD variations were reflected by the concentrations of the parameters. In the theoretical part, the objective was to provide control models for simulating staged instream aerators based on experimental data taken from the Passaic River instream aeration project. The models were computerized on an analog computer for use in obtaining oxygen-uptake rates and parameter values. As part of the theoretical investigations, the optimal instream aeration problem was formulated and analyzed in terms of Pontryagin's Minimum Principle. (WRSIC abstract)