 Reservoirs have been built for various purposes such as water supply, irrigation and electricity generation in Brazil. More than 700 large dams and associated reservoirs exist in the country's major rivers. These reservoirs bring economic benefits but also cause significant alterations to natural hydrologic regimes affecting habitat quality and biodynamics. The main impact of reservoirs is the change from lotic to lentic water, which affects 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 such as construction of fish passages, fishery control and stocking have been taken to minimize dam impacts but their results are questionable or with clear failures. The Piranha River basin is the most affected by dams in Brazil and patterns in the decline of fish diversity and negative consequences in the fishery and ecosystem functioning have been described. Suggestions for improving conservation of ikthia fauna in South American basins influenced by dams are presented. This article was authored by A. A. Augustino, F. M. Pelicis and L. C. Gomez. We are article.tv, links in the description below.