Indigenous groups have opposed the dam vigorously for decades, fearing that it will upend their way of life. Environmentalists warn that the impacts of the dam—deforestation, methane emissions, and an irreparable changes to the Xingu River's ecosystem—far outweigh any benefits. The dam, which would be the world's third largest, is expected to displace 16,000 people according to the government, although some NGOs put the number at 40,000. The dam will flood over 40,000 hectares of pristine rainforest, an area about seven times the size of Manhattan.