We experienced this adventure at the Rio da Prata near the little town of Bonito. Due to the calcium carbonates in the water all the particulate materials are absorbed and sink to the ground. That's why the water in the rivers is cristal clear and nature developed an amazing unterwater world. For the visitors it is just three hours of floating through another world.
As an exception the underwater pictures were not taken by us! And that's how it happened: Due to mz stinginess I didn't want to spend the 20 Euros for renting an underwater camera. But when I put on the diving glasses the first time I just wanted to freak out ... but it was too late!