There are five species of river dolphin, two South American and three Asian, all of which are endangered. The tucuxi Sotalia fluviatilis is not a true river dolphin, but lives in the Amazon and Orinoco rivers, as well as in coastal waters. As a result of living in muddy water, river dolphins' eyes have become very small. They rely on echolocation to navigate and find food. All dolphins power themselves by beating the tail up and down, and use the flippers to steer and stabilize.
Dolphins have great learning ability and are popular performers in aquariums.
The US Navy began training dolphins for military purposes in 1962, and in 1987 six dolphins were sent to detect mines in the Persian Gulf. Marine dolphins are endangered by fishing nets, speedboats, and pollution. In 1990 the North Sea states agreed to introduce legislation to protect them.