There are a lot of point and shoot cameras that are waterproof right out of the box, but they usually only safe to a depth of a few feet.
However, in most situations, just a foot or two below the surface is plenty for great underwater lifestyle photography.
Then, there are waterproof plastic bags that are designed to protect a camera while underwater.
This style of waterproof housing has the advantage of being generic, so that different cameras can be used with different housings. I use an EWA Marine U-BXP100 housing which has a glass port and even has room for an on camera flash.
There are also Outex underwater camera housings, which are pretty similar.
The big disadvantage with camera-in-a-bag type underwater camera housings is that it is nearly impossible to change any settings while your camera is in the bag.
Finally, there are hard cases.
Hard case underwater camera housings from manufacturers such as Ikelite or Sea&Sea are by far the best quality and easiest to use.
Unfortuantly, hard case underwater camera housings are pretty pricy, and they are camera specific – meaning if you bought a hard case underwater camera housing for your Canon 5D Mk II – its not going to work with your new Canon 5D Mk III.
Light behaves much differently underwater than it does in air.
The biggest difference is that different wavelengths of light have different abilities to penetrate through water.
Light in the red spectrum travels the shortest distance through water, while blue light travels the furthest.
What that means for underwater photography is that the further the distance is between your subject and your camera underwater, the less red light will be captured by the camera – which is why things look blue underwater.
Underwater shooting has gone from a near to impossible outcome, to an everyday, fun in the sun adventure. Such I want to eventually get into underwater photography (living closer to the Ocean) it's good to know that there are a few tricks to playing with the light under the surface.