Pacific salmon (Oncorhynchus spp.) rearing in lakes and reservoirs have been known to become heavily infected with an ectoparasitic copepod (Salmincola californiensis). Little is known about the factors that affect the parasite infection prevalence and intensity. However, previous research suggests that the parasite may negatively affect the fitness and survival of the host fish. I determined the effect of water temperature, stress, and the density of the free-swimming infectious stage of S. californiensis, the copepodid, by experimentally exposing juvenile Chinook salmon (O. tshawytscha). I also evaluated the potential for cross infection by placing naïve and infected fish in the same tank for 10 weeks. The ability to osmoregulate and transition to seawater was investigated by placing unexposed and exposed fish in 34 ppt seawater and monitoring for 24 hours. I achieved infection rates observed in wild populations under certain treatment conditions: warm water (15-16oC) and high copepodid densities (150-300/L). I also observed mortality rates of 4-5% associated with copepod infection intensity during the infection experiment. Cross-infection was achieved but at much lower infection rates. Juvenile Chinook salmon exposed to copepodid parasites experienced high mortality rates (26.7-54.5%) compared to control fish (0-8%) and could not regulate plasma Na+ concentrations back down to normal when transitioned to seawater. Our findings suggest that performance, survival, and seawater transition of juvenile Chinook salmon is negatively impacted by exposure to S. californiensis. Recovery efforts for juvenile Pacific salmon rearing in reservoirs could be hampered by the presence of S. califroniensis.