This is an Amazon river dolphin, more commonly referred to as a boto or bouto.
Out of the extant species of river dolphins, the boto is the largest (although still considerably small for cetaceans) and females can grow up to about 8 feet long. Males are usually smaller. Like other river dolphins, the boto has unfused neck vertebrae, meaning that unlike most other cetaceans, it can move its head independently of its body. This characteristic probably evolved to help the boto (and other river dolphins) navigate the shallow river basins during dry seasons. Another interesting characteristic to the river dolphin, is that they have a long, almost prehistoric looking snout, which they use to pry their prey (usually fish and crabs) from sunken logs and river vegetation.
You may have noticed that the boto in the image is a pale pink color; depending on the age of the dolphin, their color can vary from grey, to pale pink, to bright pink. Young dolphins are grey in color, and as they grow they turn gradually more pink. Eventually, the dolphin reaches a point where their pink color fades; an adult dolphin will appear almost white. There are currently three recognized subspecies that vary in color, size, location, and number of teeth.
Like most other cetaceans, the Amazon river dolphin uses echolocation to find prey and navigate its surroundings. While hunting, the boto will swivel its head from side to side in a scanning technique, something that is made possible by its unique neck vertebrae.
Botos are curious by nature, and they tend to approach boats. This is something that has turned into a problem, as it makes the boto an easy and willing target for natives to capture and kill. They are frequently used as bait to fish for giant catfish. Here is a good article about the present day conservation struggles faced by the boto. Dolphins (and especially river dolphins) do very poorly in captivity, so the only thing that can be done to help the species is encourage the natives to stop hunting them to the point of extinction.