The Rio Napo which is a major tributary of the Amazon River forms many oxbow type lakes. Sacha Lodge in Ecuador is located on one of these. Interestingly you can both swim here and fish for piranha. The piranha species found here tend to be small and apparently mostly eat fruit, seeds, and small birds that fall into the water. They have razor sharp teeth and also can eat other fish and small mammals and larger injured mammals. Also during some of our dusk and dawn canoe rides we were accompanied by fish eating bats.