 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 large rivers. These reservoirs bring economic development but also alter 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 fishes. Fish species richness usually increases immediately after reservoir formation but decreases as they age. Dams promote discharge control, altering seasonal flood cycles. Most affected species are re-aphilics and long-distance migratory that require distinct habitats to fulfill their life cycles. Management actions such as fish passages, fishery control and stocking have been taken to minimize dam impacts in Brazil but results are questionable or with clear failures. The Piranha River basin is the most affected by dams in Brazil and negative consequences include alteration and decline in fish diversity, fishery and ecosystem functioning. Suggestions for improving conservation of ikthia fauna in South American basins influenced by dams include better management actions, monitoring and restoration efforts. This article was authored by A. A. Augustino, F. M. Pelicis, and L. C. Gomez. We are article.tv, links in the description below.