Tourists were left panicked at a holiday resort after the ocean turned blood red overnight - leading many to believe that somebody had perhaps been attacked by a shark.
Pictures of a crimson tide crashing onto the beach in Shenzhen, in China's Guangdong province, left some thinking there'd been a shark attack, or perhaps that Judgement Day had arrived.
According to the Mirror, biblical texts forewarn that a blood red sea is one of the ten plagues of Egypt marking the End of The World.
But the reality behind the colour change was far less gruesome or mysterious.
Thousands of algae blooms that change colour to deep red when reproduced in one area were responsible for the ocean's alarming change of hue.
According to the Express, local environment official Kang Ts'ai said: "Although it is harmless, we have nevertheless slapped a ban on any swimming or watersports in the area until the algae is swept back out to sea."
The paper adds that algal blooms are a natural occurrence, but can be increased by pollution in coastal areas, as well as being a sign of climate change.
Shenzhen's Monitoring Centre for Marine Environment and Resources experts said the algae should disappear once the water temperature had lowered.
According to Wikipedia, red tide is a common name for a phenomenon known as an algal bloom (large concentrations of aquatic microorganisms) when it is caused by a few species of dinoflagellates and the bloom takes on a red or brown color.
Red tides are events in which estuarine, marine, or fresh water algae accumulate rapidly in the water column, resulting in colouration of the surface water. It is usually found in coastal areas.
Some red tides are associated with the production of natural toxins, depletion of dissolved oxygen or other harmful effects, and are generally described as harmful algal blooms. The most conspicuous effects of these kinds of red tides are the associated wildlife mortalities of marine and coastal species of fish, birds, marine mammals like manatees, and other organisms.