Grant County Public Utility District (PUD) owns and operates the Priest Rapids Hydroelectric Project, including the Wanapum and Priest Rapids Dams, located on the mid-Columbia River in central Washington. A 401 Water Quality Certification (401 WQC), incorporated into the FERC license for the project, required evaluation of project compliance with water temperature standards. NHC developed and calibrated a CE-QUAL-W2 model of the reservoir formed by each dam and a portion of the Hanford Reach below Priest Rapids Dam. A set of “without project” models was also developed and applied to evaluate the project’s impact on water temperature by simulating the same reach of river without the dams in place. Modelling demonstrated that the project passed the 401 WQC requirements, indicating that the temperature effects of the dams are within the state water quality standards for protection of aquatic species.