A river in China deemed clean enough to drink has turned red overnight, mystifying the city’s residents and officials alike. Locals claim the phenomenon has never happened before and industrial contamination has been dismissed as a viable option.

People in the area filled water bottles with water from the river located in Xinmeizhou village, Cangnan County in eastern China’s Zhejiang province.

Early on Thursday morning the water looked normal. “But then suddenly, within the space of a few minutes, the water started turning darker and eventually was completely red,” Local Na Wan told the Daily Express.

We have always been able to catch fish and you can even drink the water because it’s just normally so good,” he added.

Nobody immediately gave a reason for the river turning red, but Wenzhou Environmental Protection Bureau inspectors have taken samples for analysis, reported China Radio International.

According to a local contacted by the station, nothing of the kind had ever happened before and there was no chemical plant upstream.

However, in September 2012, the Yangtze River mysteriously started running red. At that point people considered industrial pollution or silt being churned up as possible causes.

After a few images were reviewed, however, scientists suggested the cause could have been more man made.

Emily Stanley, a professor of limnology (the study of inland waters) at the University of Wisconsin told LiveScience at the time:

“It looks like a pollutant phenomenon,” she said. “Water bodies that have turned red very fast in the past have happened because people have dumped dyes into them.”

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