"The warmth of the water and the visibility is incredible, so you can see the whole ship from the surface, " says Easterbrook.

CNN: A worthy wreck for divers: USS Kittiwake

Even when the sharks are found closer to the ocean surface, they spend their time in the cool-temperature, plankton-rich waters that limit underwater visibility and make diving difficult.

CNN: Scientists discover winter home of world's second-biggest fish

And we have rope tenders that control us on the surface and give us particular signals and tell us where to turn and things of that nature, because with no visibility you normally will lose your sense of direction and everything else.

NPR: River Poses Hazard for Dive Teams