The phenomenon of hydrosphere this one happening in Cenote Angelita located in Caribbean waters of Mexico. Cenote in Mayan language means cave, so actually it is shaded by a layer of hydrogen sulfide formed from organisms rotting in the cave.
Piles of it forming a wall that restricts ocean water and fresh water and was given the name of the halocline. The phenomenon of the halocline is vertical in the Sea zone that occurs because of a difference of pressure layer of water so that the salt levels dropped dramatically and make the water becomes fresh.