A canal in greater Buenos Aires, Argentina, turned a striking red on Thursday, sparking alarm among residents who feared a toxic spill was responsible, according to the BBC.

Videos and photographs captured the vividly coloured water flowing into the Río de la Plata bordering an ecological reserve, raising concerns over potential contamination.

Soon after, the canal turned red local resident talked with media to express the fears on pollution and environmental hazards

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

A woman called Silvia, told local news channel C5N that although it is has turned red now, “other times it was yellow, with an acidic smell that makes us sick even in the throat”.

She added: “I live a block from the stream. Today, it has no smell. There are not many factories in the area, although there are warehouses.”

Another resident, Maria Ducomls, told AFP industries in the region dump waste in the water, and said she had seen it coloured differently in the past — “bluish, a little green, pink, a little lilac, with grease on top”.

Authorities collected water samples from the river to determine the cause of the discolouration.

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

According to AFP, by late afternoon the colour of the water had lost some of its intensity.