The Yangtze River, China’s largest river, is known as the Golden Watercourse, but residents along its shores noticed this week that the water wasn’t its usual hue, rather the water had turned red, and no one seems to know why.

ABC News reported that the river turned red on Thursday near the city of Chongquing, where the Yangtze meets the Jialin River. Some residents were stumped by the turn of events, stopping to collect the water in bottles as a keepsake. A photo showing a man with water from the river in a clear plastic bottle made the water look almost as brightly colored as tomato juice. Others, like fisherman and thos working on boats went about their usual daily business. reported that the river was reported as having turned red by people at various spots along its course, and added that local officials are investigating, but do not know why the Yangtze river turned red.

The UK Daily Mail reported that this isn’t the first time a Chinese river turned red. The Jian River experienced a similar event last December when it was polluted by a powerful dye that was being illegally dumped. Officials raided and shutdown the factory responsible.