Water quality simulation, using the model of Streeter and Phelps, were made to define deoxygenation rates (kd) and aeration rates (ka) for the Sinu River. Historical data of eight years of follow-up (2000-2007) of Biochemical Oxygen Demand (BOD), total nitrogen Kjeldahl (NTK), dissolved oxygen (DO), temperature and flow rate were taken at 10 stations located along the River. Once calibrated the model was validated with data collected from 2008 to 2014. It was noted that the stations near the dam and the lake complex of Lower Sinu had higher values of kd and lower ka, nevertheless, acceptable for rivers with little pollution. The coefficients vary depending on the section, the flow and temperature throughout the year. However, this coefficients show that the Sinu River is a stream with low levels of pollution and with a high potential for self-purification.