Pacific salmon use olfactory cues to locate their spawning grounds. Past homing research has explored various aspects of the olfactory system, such as the imprinting process, but the mechanisms through which olfaction drives homing remain largely unknown. Genomics studies provide a novel approach to homing research, allowing us to investigate how olfaction and alterations to flow regimes that result from hydroelectric development mediate homing from a molecular level. Olfactory receptors (ORs) located in the olfactory epithelia detect odorants in the external environment. These receptors initiate the olfactory process, and expression of OR genes therefore strongly influences route selection during the spawning migration. We examined the expression of OR genes in a population of early summer Fraser River sockeye at the site of a hydroelectric dam. Due to diversions caused by the dam, chemical cues originating from the natal tributary are diluted by water that enters the system from a different watershed. We held sockeye in the river containing their home stream water and in the river that originates from the different watershed. We then used quantitative PCR to determine whether the absence of natal chemical cues alters olfactory gene expression. In addition, we analyzed olfactory gene expression of sockeye exposed to an artificial stressor event, to determine whether stressful events such as fishway passage or blocked waterways affect olfactory gene expression.