Fishway Performances in South American Regulated Rivers

South American river basins have high fish diversity and contain many economically important migratory fish species. Approximately 140 dams have been built, and 280 dams are planned for the near future in De La Plata River basin. Adult fish passage facilities in the basin are restricted to a few low-head dams in Brazil that have pool-weir systems of modest effectiveness, passing primarily migratory species (e.g. Prochilodus). A historical reliance on stock maintenance through hatchery production has hindered development of fish passage technology. In the lower basin a Borland lock system was installed at Salto Grande Dam and fish elevators were installed at Yacyreta Dam. Both systems have limited success in passing migratory fishes. The limited success of fish transfer systems in the basin can be attributed to unquestioning acceptance of North American fish passage technology without consideration of the unique biology and behavior of South American fishes, inappropriate entrance geometry and location, and inadequate scaling of fishways relative to numbers of fish that must be passed to sustain stocks of migratory fishes. We advocate an integrated approach to develop and improve fishways based on ecological, hydraulic, and engineering criteria developed specifically for basin fishes supplemented by other strategies such as hatchery production and passage through navigation locks.