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 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 small river in greater Buenos Aires was dyed a deep and worrying shade of red on Thursday after what is thought to have been a leak of dye from a nearby factory.