As you gaze at the vast construction site for the Santo Antônio hydroelectric dam on the Madeira river in the far west of Brazil, it is hard to believe the project has been designed to minimise its environmental impact.

The companies behind the R$13.5bn (US$7.7bn) development, including Furnas, the electricity company that is part of the state-owned Eletrobras group, and Odebrecht, the construction company, describe it as the largest private sector civil engineering project underway anywhere in the world.