The present study involves the application of a water quality model QUAL2K for developing the BOD-DO model and evaluation of the results for a 50 km stretch of river Ghataprabha near Mudhol town of Bagalkot district, Karnataka. QUAL2K is a modeling framework for simulating river and stream water quality. Arc-GIS technique is used to obtain some hydro-geometric data of the river for input to model QUAL2K. For calibration and validation of the model, the BOD and DO values were monitored at six different locations. The calibrated model was validated to predict water quality using a different set of data under different conditions. The performance of the model was evaluated using statistics based on Standard errors (SE), Normalized Mean Errors (NME) and Mean Multiplicative errors (MME). The SE and MME values for BOD and DO during calibration are, 1.41 (1.12) and1.28 (0.90), respectively. The values in the bracket show MME. Corresponding values for the validation are 1.27 (1.09) and 1.10 (0.96). These results show that the values predicted by the model are in close agreement with measured values.