The animals make these sounds in air-filled sacs connected to their blowholes. Dolphins also communicate by slapping their flukes on the surface of the water. Swimming and diving. Dolphins swim by moving their flukes up and down. This action differs from that of most fish, which propel themselves through the water by swinging their tail fins from side to side.
Dolphins use their flippers to make sharp turns and sudden stops.
But they can maintain those speeds for only a short time. Most dolphins swim much slower. Dolphins do not usually dive deeply, though they have the ability to do so. When a dolphin dives, its lungs collapse and its heart rate slows down. These actions allow the animal's body to adjust to the increasing pressure as the dolphin dives deeper underwater.