Usable capacities of thermoelectric power plants are constrained by the water availability and temperature of cooling water. Climate change and water management affect stream temperature and generate further influence on thermoelectricity production. This study investigates the relative impacts of climate change and water management, including reservoir operation and local water withdrawal, on stream temperature and thermoelectric production. The Model for Scale Adaptive River Transport (MOSART) coupled with a Water Management (WM) module is adopted to simulate the heat transport along with water flux and the energy exchanges between river water and the atmosphere. It is found that water management helps mitigate the stream temperature rise pace especially for arid and semi-arid basins in the western U.S. through inter-annual water redistribution and alleviate the amplitude increase of stream temperature caused by climatic changes. Moreover, our results suggest that water management can reduce power plant usable capacity loss caused by stream temperature increase in the future by as much as that achieved through emission mitigation that reduces global warming.