The showdown in the suburbs of the capital of Argentina Buenos Aires became bright red on Thursday, alarming locals.
The Sarandí Channel passes through residential districts and industrial areas before reaching the mouth, Rio de la Plat, which borders with an ecological reserve.
Local media reports suggest that the color may be caused by disposal of textile color or chemical waste from a nearby warehouse.
Authorities took samples to determine the source of pollution.
Read more: Argentine channel becomes bright red
