The reaeration capacity of the Rock River from Lake Koshkonong, Wisconsin, to Rockton, Illinois, was determined using the energy-dissipation model. The model was calibrated using data from radioactive-tracer measurements in the study reach. Reaeration coefficients (K2) were computed for the annual minimum 7-day mean discharge that occurs on the average of once in 10 years (Q7,10). A time-of-travel model was developed using river discharge, slope, and velocity data from three dye studies. The model was used to estimate traveltime for the Q7,10 for use in the energy-dissipation model. During one radiotracer study, 17 mile per hour winds apparently increased the reaeration coefficient about 40 times. (Woodard-USGS)