I don't know how accurate Wiki is, but here is what they say on the topic:
Plans for the dam began in 1975 but were soon shelved due to controversy; they were later revitalized in the late 1990s. In the 2000s, the dam was redesigned, but faced renewed controversy and controversial impact assessments were carried out. On 26 August 2010, a contract was signed with Norte Energia to construct the dam once the Brazilian Institute of Environment and Renewable Natural Resources (IBAMA) had issued an installation license. A partial installation license was granted on 26 January 2011 and a full license to construct the dam was issued on 1 June 2011.
https://en.wikipedia.org/wiki/Belo_Monte_Dam
I would say that the claim the dam started in 1975 is a bit specious. That 20+ year gap between when somebody had an idea and when that idea was acted upon would indicate that it was never really serious in the 70s. Brazil needed that two + decades to get its corruption to a level where it could actually start harming the planet effectively. (My personal take on things.)
I am no genius but even I can figure out that the best way to avoid being guilty of driving any species to extinction is the ability to deny that species exists. And to make that stick, make sure no studies are done that might indicate anything to the contrary.
Species exist before they are actually described. The zebra was described in 1991, how many years before that were the people who ply the Big Bend aware of its existence?
I would note the following example in this respect:
REVIEW OF THE GEOGRAPHIC DISTRIBUTION OF FISH FAUNA
OF THE XINGU RIVER BASIN, BRAZIL
Mauricio Camargo, Tommaso Giarrizzo & Victoria Isaac
Laboratório de Biologia Pesqueira e Manejo de Recursos Aquáticos, Universidade Federal do Pará,
Belém, Brazil
Abstract. This study is a comprehensive review of fish fauna data for the Xingu River system. Information was compiled from seven field surveys (conducted between 2001 and 2002), bibliographic references, and museum collection records. To provide data on the spatial distribution of fish species, the river basin was divided into six areas according to geographical and hydrological characteristics. Fish species from 14 orders and 47 families were recorded; the most diverse orders were Characiformes (210 species), Siluriformes (146 species), Perciformes (62 species) and Gimnotiformes (20 species). Of the 467 species identified, 69 were common to the whole river basin. Based on these results, two priority conservation areas were identified: 1) headwater rivers, which are characterized by a diverse range of small characid and cichlid species and intense anthropogenic disturbance, and 2) middle section of the Xingu, from its confluence with the Irirí River to its downstream waterfalls near Belomonte village. This region is characterized by a high diversity of Cichlidae, particularly Teleocichla, Anostomidae and Loricariidae families. Conserving these areas will help to maintain hydrological connectivity of the Xingu River system. Accepted 17 October 2004.
https://www.google.com/url?sa=t&rct=j&q ... CBcrZyhdyA
I guess the folks in power in the Brazilian government and the folks at Norte Energia had not yet learned to read at that time. Or maybe it was they just could not see though all the piles of money they imagined would be coming their way?
Consider the long term history of the earth and all the species that have ever lived. Species cease to exist, but the planet still remains. The human species is no exception in this respect.
