 Reservoirs have been built for water supply, irrigation and electricity generation in Brazil. There are over 700 large dams and associated reservoirs in the country's major rivers. These reservoirs promote local and regional economic development, but also cause significant alterations to natural hydrologic regimes affecting habitat quality and biode dynamics. The main impact of reservoirs is the change from lotic to lentic water, which influences aquatic fauna, including fish. Fish species richness usually increases immediately after reservoir formation but decreases as reservoirs age. Dams also promote discharge control, altering seasonal flood cycles. Management actions taken to minimize dam impacts include fish passages, fishery control and stocking. However, these actions have been questionable or unsuccessful. The Piranha River basin in Brazil is the most affected by dams. Fish diversity has declined in areas influenced by dams, leading to negative consequences for the fishery and ecosystem functioning. Suggestions for improving conservation of ikthia fauna in South American basins include better management actions and more research on the impacts of dams on fish populations. This article was authored by A. A. Agostino, F. M. Pelicis, and L. C. Gomez. We are article.tv, links in the description below.