The Dolphins The Ganges river dolphin has become almost blind. The river water is so muddy, it find fish by making sounds and listening for echoes-just like a bat. There are more than 30 kinds of dolphins in the oceans and rivers. They are all superb swimmers. Dolphins swim together in large groups called schools, leaping high out of the water as they play. If one injured, the other help it to the surface to breathe. When a bottle nose dolphin has a baby, several females gather around to protect her.