A wastewater containing no dissolved oxygen and 60 mg/L of easily degradable organic compounds with an average chemical formula of C8H18O5 is discharged at a rate of 2 m3/s into a river that has an upstream flow rate of 7 m3/s. The average cross-section of the river is 18 m2. The water upstream of the discharge point has an ultimate BOD of 4 mg/L and contains 8.0 mg/L DO. The rate constants for BOD utilization (kd) and reaeration (kr) in the river are 0.14 d-1 and 0.30 d-1, respectively. The Henry's Lawconstant (kH) for oxygen under the ambient conditions is 10-2.77 mol/L-atm.