A bright pink lagoon is setting off red alarms for environmentalists in southern Argentina

The pond is one of several located about 20 miles from the city of Trelew used by local industries for releasing chemicals or treated water.

Pablo Lada, a member of the SocioEnvironmental Assemblies of Chubut province, called for an independent analysis to determine what is to blame.

Mr Landa said the water had taken on a rosy hue before, but “now it is striking; it is an intense pink”.

He said specialists suspect it is caused by sodium sulphite, used to help preserve shellfish.

Provincial officials have said they expect the colour to disappear in a few days.

Some local media have blamed a consortium from the regional capital Rawson, suggesting it dumped chemicals there because neighbours closer had complained about the smell.

But Adriana Sanz, in charge of water treatment for the Rawson Ambiental company, denied that and suggested it was part of a campaign by an unspecified rival company to damage Rawson’s reputation.

She said her company uses a separate pond about half a mile away for its discharges of treated water and that the one that turned pink is used by the Trelew Industrial Park.