The report represents a study of the prediction of water quality for the Upper Wabash River Basin. The basin studied involves an 8208 square mile area above Covington, Indiana. A significant conclusion was that with the present systems, a general predictive model from one basin to another cannot be used. A predictive model is proposed for the specific basin. The equation used considers the diurnal photosynthetic effect on the dissolved oxygen deficit. Sensitivity studies indicated that for values of river BOD removal and reaeration coefficients determined from field observed data and for all flow and loading regimes, algae are a detriment to the maintenance of a minimum dissolved oxygen concentration. The mathematical model developed does provide a basis for further field studies and a framework for additional sensitivity analyses from both a spatial and temporal aspect.