Diel dissolved oxygen DO concentrations and temperature were sensed at high-frequency and modeled in an eastern Iowan stream, Clear Creek, in an agricultural setting. The magnitude of the diel changes in DO and temperature were largest at the upstream headwater station. Inclusion of temperature change factors increased the accuracy of modeling results and yielded estimates of the reaeration rate constant, primary production rate, and respiration rate. The DO modeling of the high-frequency measurements 15-min intervals revealed a temperature-driven nonlinear reaeration process that led to increases in nighttime DO concentrations. The DO modeling results from three sensing stations in the watershed revealed decreasing trends in primary productivity, respiration, and the reaeration rate constant with increasing drainage area. Light extinction from suspended solids was the main factor limiting net primary production. As a result, the P/R ratio also decreased with increasing drainage area. High-frequency sensor data and DO modeling revealed the effects of temperature and watershed scale on the primary factors that dictate diel DO dynamics in a stream setting.