There are various types of gadgets that come already waterproof. You can get a digital camera that works almost as well underwater as it does above. Special casing keeps the water out and lets you snap away multitude of cool and fun things in the water. And while taking those shots, you can now also enjoy some music with waterproof music players such as the Freestyle 2gb mp3 player
For other gadgets there are cases of different shapes and sizes that would protect them in the water or from any splashes around the water.
OverBoard Waterproof Gadget Cases are 100% waterproof and float if dropped in water. They are perfect for safeguarding your gadgets (phone, camera, MP3 player) and also keep out dust, sand and dirt.
There is one for the camera that lets you take pictures down to 19ft (6m) underwater and is perfect for digital cameras without a telescopic zoom lens. And an MP3 case that is heavy duty waterproof padded with an arm strap, which would definitly come in handy under water with the currents.
The coolest and definitly useful waterproof gadget I found is the Underwater Camera and Video Diving Mask