The Sarandí River in a suburb of the Argentinian capital Buenos Aires turned bright red on Thursday. Videos show the water glowing an intense red.
According to local media reports, the color could have been caused by the discharge of textile dyes or chemical waste from a nearby depot.
The Ministry of the Environment announced in a statement that water samples had been taken from the Sarandí Canal to determine the cause of the color change.
En avellaneda, el arroyo sarandi se tiño de rojo sangre como en las 10 plagas de Egipto
By late afternoon, the color of the water had lost some of its intensity, reports the AFP news agency.
Residents have claimed that many local businesses are dumping toxic waste in the water.
The river used to glow yellow
One resident told the local TV station "C5N" that although the water has now turned red, "it used to be yellow and had a sour smell that even made you feel sick in your throat".
🇦🇷🩸River of Blood: Sarandi Runs Red in Argentina
Locals fear toxic materials have turned the waterway - which runs into the Rio de la Plata in the outskirts of Beunos Aires - blood red. Authorities have taken samples to discover the source of contamination. pic.twitter.com/J8ioBCl1zf