To be able to shoot underwater, the usual option was to use a watertight housing that was more expensive than your point-and-shoot camera. These days, you have two more options: the Pentax Optio W20 and Olympus Stylus 720SW.
These are P&S compacts that donâ€™t need those bulky housings; you can take the camera directly into the water with you, and you can snap some underwater pictures of fish and corals as you dive with it.
The 7-megapixel Optio W20 is rated â€œJIS Class 8â€ which means you can take it to a depth of 5ft for as long as 30 minutes. The Stylus 720SW, meanwhile, goes twice deeper at 10ft but you also have to watch your time.
PopPhoto.com has a comparison review of both underwater cameras, with sample shots taken not only beneath the water but also snapshots above the water. See link below.