In the Amazon rainforest  the Brazilian government have decided to allow a massive hydroelectric dam to be built.

The Belo Monte dam would be the third largest in the world. The idea is that it will store enough water to provide electricity to twenty three million homes.

But lots of people think that building the dam is a really bad idea. They reckon that large parts of the rainforest will be destroyed in the process. Not only would that be bad for the environment - they think it would also be devastating for the indigenous tribes that live in the area.