A river in eastern China turned blood red overnight and investigators aren't completely sure why.

Residents living inWenzhou, a commercial city in the Zhejiang Province, saw the riverchange to crimsonThursday morning, China Radio International reports. People told CRI the river was flowing normally at 4 a.m. butrapidly turned a scary shade of red at about 6 a.m.A villager who has lived there his entire life said he'd never seen the river turn red before.

A boat moves along the crimson hued water Thursday in Wenzhou, east China's Zhejiang Province.

(STR/AFP/Getty Images)

ABC News reported thatresidents also experienced a strange smell in the airas the river changed color.

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After investigating the incident, theWenzhouEnvironmental Protection Bureau told Voice of America thatthey were unable to figure out the causeof the river's change in hue. Investigators said they didn't find anything suspicious coming from the factories along the river.

One theory from the bureau was that someone dumped artificial coloring in the water, believingheavy rains from TyphoonMatmowould wash away the red dye, China News reported.But the Typhoon did not dump heavy rain on the area as some expected, so the river became "bloodied," according to that theory.

This is the third time in three yearsa river in China has turned red, Mashable reports. The website addsthat the Yangtze River in Chongqing turned a lighter shade of red in 2012, and in 2011, the Jian River in Henan Province turned dark red.

Although investigators haven't pinpointed what happened Thursday inWenzhou, experts are offering possible explanations for previous cases.After the 2012 incident, the University of Wisconsin's Emily Stanley, professor of limnology​— which is the study of inland waters​—told LiveScience.com the sudden change of a river's color is likely man-made.

"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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