The Santo Antônio and Jirau dams, under construction on the Madeira River, will have significant impacts, including flooding in Bolivia due to the Jirau reservoir's backwater stretch. The reservoirs eliminate natural ecosystems, and the dams block fish migration affecting both biodiversity and commercial production, especially of the giant catfish of the Madeira River that are important resources in Bolivia and Peru as well as Brazil. Changes in flooding regimes in downstream várzea (floodplain) lakes will also affect fisheries. Mercury methylation and greenhouse-gas emissions are additional problems. The reservoirs form part of a planned series of waterways that, if completed, would open large areas in Bolivian Amazonia to soybeans, thus stimulating deforestation. The dams have significant social impacts, including displacing riverside population and eliminating livelihoods from fishing. Despite the technical staff responsible for environmental licensing having submitted a formal opinion considering these concerns to be exceedingly serious and insufficiently studied to authorize dam construction, political appointees approved the licenses. The Madeira Dams offer important lessons for environmental control in Brazil and in many other countries facing similar challenges.