Residents living near the Sarandí have long complained about pollution in the area

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.

The violent hue of the Sarandí, which runs through the municipality of Avellenada, six miles (9.6km) south of the Argentinian capital, alarmed local residents, who have long complained about industrial pollution in the area.