At Rio Triste, 17km from Bom Jardim, you're delivered to the start of a forest trail by tractor. With any luck, you may spot some monkeys before floating face to face with red-finned piraputanga fish in a deep, clear pool. Then float downriver behind your guide, dodging submerged tree trunks and trying to spot sand-colored freshwater stingrays. You can rent an underwater camera (R$50).