A peculiar phenomenon spotted in the Russian city of Anapa on the Black Sea has puzzled social media users.
A video recently uploaded on Instagram shows sea water bubbling away just off one of the city's beaches.
"It’s got so warm in Anapa that the water is boiling by the sea," the caption reads. "Ever seen such a wonder?"
This unusual sight left a number of netizens wondering what caused it, with some jokingly comparing it to a "fizzy aspirin" tablet dissolving in water.
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Other, more down-to-earth suggestions, included a ruptured sewage pipe and a possible geyser eruption, while one person advised taking water samples for analysis to dispel the mystery.