Scuba divers from across the globe flock to Angelita Cenote, an underwater cave along the coast of the Yucatán Peninsula, to witness an unusual mirage: a river in the middle of the Gulf of Mexico.

Located about 30 meters below the water’s surface at Angelita Cenote, the “river” is actually the result of a hydrogen sulphide cloud at the halocline, the point where the saltwater and freshwater in the cave meet. Both the freshwater and saltwater came to be trapped in the cave because of a sinkhole, which was caused by a limestone collapse. Organic chemicals—which are suspended at the halocline because of the salinity change—create the foggy layer that has the appearance of a river, concealing clear saltwater beneath.

The photographer Anatoly Beloshchin took these haunting shots of the quote-unquote river.

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