It's not that difficult when you know how. Once you've learned to dive, it's a natural progression to want to bring back photographs or home videos as a memento of your experiences underwater. The underwater scenes, the shipwrecks, the animals you will meet, even the friends you dive with, will all be subjects for your camera. However, getting good photographs is a little more complicated than simply putting your camera into a plastic bag and plunging in.
Water is a lot more dense than air.
The fundamental problems of getting good pictures under water stem from this great density. At only 10m deep, the pressure is twice that of normal, so underwater camera equipment has to be immensely strong, with any points of entry such as the camera back or its battery compartment sealed with gaskets or 'O' rings. There are purpose-built amphibious cameras and specially designed marine housings for normal still and video cameras. The same goes for lights and flashguns. Because water is so dense, it also absorbs light.