Rivers, as well as rain forests, in the state of Amazonas in northwestern Brazil contain tremendous biodiversity. One tributary of the Amazon, the Rio Negro, harbors at least 700 species of freshwater fish, seven times what the Mississippi River contains. Not surprisingly, fish-loving dolphins adapted and reveled in this habitat, which slowly freshened from the remnants of an inland sea some 13 million years ago.

The Amazon River dolphin (Inia geoffrensis) has a longer beak, larger flippers and flukes, and smaller eyes than its marine relatives. It also has stiff hairs on its long beak that probably help the animal to sense, much as cat or rat whiskers function, in the dark, humus-rich waters that give the Rio Negro its name. Another adaptation that helps the dolphin hunt masterfully in the muddy shallows of the Amazon Basin is its flexible neck, which it can bend at an angle of 90 degrees, up, down, or to the sides, from its body. Of course, no observer fails to notice the dolphin’s distinctively rosy skin, thought perhaps to bloom from its diet of crustaceans, as holds true for flamingos with a diet high in beta carotene.

This past July, photographer Art Wolfe traveled twenty miles upstream from Manaus on the Rio Negro to photograph the Amazon River dolphins. Standing on a submerged platform that was suspended from a dock and situated over deep water, Wolfe held his camera, encased in an underwater housing unit, and breathed through a snorkel. The dolphins swam up to feed on small silver fish nearby.

Of all its freshwater cetacean relatives, the Amazon River dolphin has the largest population, probably numbering in the tens of thousands. The Ganges River dolphin, known for its blindness, has fewer than 1,800 individuals; the Indus River dolphin comprises about 1,100; and only 200 Irrawaddy dolphins survive in fractured habitats. In 2006 the Yangtze River dolphin, the baiji, was declared extinct.

Over the course of his forty-year career, photographer Art Wolfe has worked on every continent and in hundreds of locations. Wolfe’s photographs have appeared in Natural History on many occasions and in more than eighty books, most recently in The New Art of Photographing Nature: An Updated Guide to Composing Stunning Images of Animals, Nature, and Landscapes and The Art of the Photograph: Essential Habits for Stronger Compositions, both published this year by Amphoto Books. Wolfe maintains his gallery, stock agency, and production company in Seattle, Washington (see www.artwolfe.com).