Abstract: Fish attempting to move upstream through hydroelectric dams can be trapped and killed in turbines. Understanding fish movement patterns can provide useful insights for how to manage dam operation and maneuvers to minimize fish kill in turbines. We evaluated the movements and abundance of two migratory fish (Prochilodus argenteus and Pimelodus maculatus) most affected by turbine operation, using acoustic telemetry and cast nets in the tailrace of Três Marias Dam (São Francisco River, Brazil) from 31 October 2011 to 16 February 2012. The General Linear Models were applied in the data in order to access the influence of time period (diurnal and nocturnal) and operational discharge (turbine and spillway) on the biotic data. The majority of tagged fish left the tailrace in less than one week, however some individuals returned, performing several visits to the tailrace. The number of visits was influenced by time period, turbine and spillway discharge. Although the time period was the only important contributor to the visits performed by P. argenteus, the movements of P. maculatus were significantly influenced by the three factors. We found that whereas P. argenteus was predominantly diurnal, P. maculatus showed nocturnal habits. Additionally, visits of P. maculatus were significantly lower during minimum turbine and spillway discharge. This result agrees with temporal changes in fish abundance in the tailrace. The number of P. maculatus captured using cast nets was also significantly lower during minimum turbine discharge. These results provide hydropower managers with useful information about the likelihood of occurrence of a fish injuries/kills events since these impacts can occur in combination with fish attraction to the tailrace. With an increased understanding of the behavior and vulnerability of fish species to turbine operational maneuvers, future operational procedures of hydropower facilities may be modified and adapted in order to protect native species.