Mining and oil companies generally earn a bad reputation for their Amazon activities, but projects devised in the name of “sustainability” can have a negative impact too. Think in particular of the programme of hydroelectric dams being rolled out across Brazil. Belo Monte, the world’s fourth largest hydroelectric dam, is being built across a southern tributary of the Amazon, for instance. It has already caused the influx of tens of thousands of workers, with severe strain on local social relations. Its impact on a vast ecosystem – a major hydrological basin – will be monumental.