Do not try underwater photography unless you own a digital camera that is specifically designed to shoot underwater or a specialty underwater housing unit that protects the camera. The camera must be sealed to protect it from water, or it will be ruined.
Underwater housings are made for both point and shoot and digital SLR cameras. Underwater housings are made specifically for certain models of cameras. Not every model of digital camera has a corresponding underwater housing unit available. Keeping your underwater equipment maintained and clean is vital to successful results.