Dolphins are mammals that live in cold water, warm water, salty water, and fresh water.  Dolphins can swim at speeds up to 25 miles per hour.  They jump to search the surface for signs of birds or schools of fish.  They also jump to frighten the fish into tighter groups, to communicate, to shake off parasites, or just for the fun of it (educated guesses).  Some dolphins can leap more than 20 feet in the air and can dive as deep as 500 feet to 1000 feet!  The dolphins average of staying under water is about 10 minutes.  Dolphins use echolocation and sound to perceive their world.  They use clicking sounds.  Tissues in the dolphin's forehead focus's the sound to which direction the dolphin wants to see.  This sound will pass through the water than strike an object and goes back to the sender.