A river in China that's normally considered quite clean turned blood red in just an hour last week.

Residents were shocked at the turn of events, in part because there are no factories or chemical plants in the area and it was considered unpolluted.

PHOTOS: Rare Sight: Colorado River Reaches Gulf

The water looked fine, residents said, early in the morning last Thursday. But then about 200-300 meters of the river began turning red and had a strange smell.

"The really weird thing is that we have always been able to catch fish and you can even drink the water because it's just normally so good," local Na Wan told NBC News. "Nobody has any idea how it could have ended up being polluted because there are no factories that dump anything in the water here."

VIDEO: Amazon River Monsters

NBC reported that experts were on the scene taking samples and one suggested that the cause was likely some sort of dye that had been dumped in the river.

Photo: A view of the red river in Xinmeizhou village, Longgang town, Cangnan county, Wenzhou city, east Chinas Zhejiang province, on July 24. Credit: Ni yanqiang/Corbis

via NBC News, Imaginechina