The channel in the suburbs of the capital of Argentina Buenos Aires became bright red on Thursday, alarming locals.
Pictures and videos show intensely colored water poured into the estuarium, 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.
The Ministry of Environment in the statement said the water samples were taken from the Sarandí Channel to determine the cause of color change.
By the late afternoon, the water color lost part of its intensity, the AFP news agency reported.
Residents claimed that many local companies lay a toxic waste into a fruit road, which passes through the area of skin processing and textile factory, about 10 km (6 miles) from the center of the capital.
A resident, a woman called Silvia, told the local newspaper C5N newspaper, that, although she had now become red, “the second time was yellow, with a sour scent that even got sick of our throat.”
“I live a block from the stream. There is no smell today. There are not many factories in this area, even though there are warehouses.”
Another resident, Maria Ducols, said AFP Industries in the region inserted waste into the water and said she saw in the past that she was colored differently – “bluish, a little green, pink, a little lilac, with fat on top”.
