A river in the greater Buenos Aires, Argentina, turned an intense red on Thursday, alarming residents who suspected toxic spills were to blame, according to local reports.

Authorities collected water samples from the river, which flows into the Rio de la Plata and borders an ecological reserve, to determine the cause of the discoloration, local media reported.

Residents speculated that the red hue might be due to aniline contamination or chemical waste from a nearby depot.

The municipality, alongside the Buenos Aires Environment Ministry said it was investigating, and initial reports suggested the substance may not be toxic.

(Production: Miguel lo Bianco, Hugo Monnet)