Underwater photography is a hobby that takes a lot of skill and money. First you have to get certified to scuba dive. Then you have to acquire special waterproof cameras and flash equipment. Next you have to have the funds to fly to your destination, rent your underwater gear and charter a boat and guide. Finally you swim around hoping to luck up on something really cool that will impress your friends. 

Or you can go find a really big aquarium like I did.