A stream winding through a populous area on the outskirts of Buenos Aires has turned crimson red in recent hours, sparking fears of industrial chemical dumping, images shared by residents on social media showed Friday.

A stream south of the Argentine capital turned a freakish vermilion this week, prompting concerns about pollution. Officials said it could be the result of “some type of organic dye.”

A river on the outskirts of Buenos Aires turned red on Thursday, causing alarm among locals. (AP video shot by: Victor R. Caivano)