Cenote Angelita or “Little Angel” is a hidden underwater river in in Mexico’s Yucatan Peninsula. The ‘river’ is due to a phenomenon called a halocline. Water with different salinity form layers underwater. Cenote Angelita is actually made of fresh water until about 29 meters when it switches to a 1-meter layer of hydrogen sulfide, after which the entire cave bottom is filled with saltwater from 30 to 60 meters deep. Diver and underwater photographer Anatoly Beloshchin has documented this phenomenon in great detail. He never dives without his trusty camera, some lights, and a fishing pole – just in case.
Take a peek at his blog.