Diving. Diver in a restriction, or narrowing, in an underwater cave. This diver is using a rebreather. This apparatus recycles the gas exhaled by the diver, making it available for reuse instead of venting it into the ocean. Rebreathers extend the range of a dive since the total dive time is less limited by the amount of gas the diver can carry, when compared with scuba tanks. For this reason rebreathers are popular for use in cave dives, as they prevent the diver running out of air if he becomes lost or trapped in a restriction. Photographed in Turtle Cavern, Palau Sipadan, Malaysia.