We use a hydrologic model coupled with a stream temperature model and downscaled general circulation model outputs to explore changes in stream temperature in the Columbia River basin for the late 21st century. On average, stream temperatures are projected to increase 3.5 °C for the spring, 5.2 °C for the summer, 2.7 °C for the fall, and 1.6 °C for the winter. Our results capture the important, and often ignored, influence of hydrological processes on changes in stream temperature.