During a night excursion on the rivers that feed into the Amazon, you suddenly see a red glow on the water’s surface. These are the eyes of a caiman as it searches for a meal. These reptiles are similar to both the crocodile and the alligator in appearance and behavior., but are more closely related to alligators. Caiman prefers freshwater, so are found in rivers. Those in the Ariau River, a tributary of the Rio Negro, measure from around 3 to 8 meters in length.