Argentina, the mystery of the blood-red waters in Mar del Plata: “External heating. Actually, no”

Argentina, several Atlantic beaches are the subject of a real invasion, a red tide that, in the height of summer, is caused by the proliferation of macroalgae.

On the peak day so far, yesterday, in several beach resorts, including the renowned Mar del Plata (420 km south of Buenos Aires), the algae gave off, after several hours spent in the sun on the sand, a strong odor, enough to annoy the bathers quite a bit. "It is a natural phenomenon that here we call +arribazones+ (more or less mega-insurgences ed.) of macroalgae", Ricardo Silva, marine biologist at the National Institute for Research and Development of Fisheries (Inidep), told the France Presse news agency. These algae, he explained, "live attached to rocky materials" underwater, but can detach under the effect of strong wave motion and the currents "make them drift towards the coast".

This is not an unusual phenomenon in the summer months, “but this summer there have been more of them,” he notes. We cannot say for sure that this proliferation is linked to climate change, Silva said, citing in particular the increase in “atypical winds” from the northeast. But “if we studied it more over time, over the years, we would definitely find a relationship,” the researcher concluded.

Eight days ago, a lake in northeastern Argentina turned green - and with it its inhabitants, the large Cabiaï rodents: the effect of cyanobacteria, a microalgae phenomenon in this case, natural but whose increase is partly linked to global warming. But on Friday, the images of the blood-red waves of the Atlantic in the media were above all reminiscent of the impressive pollution - human, this - of a waterway on the outskirts of Buenos Aires, ten days ago.

A few hours earlier, the "Sarandi", a partially canalized watercourse, had turned carmine red, causing concern among the inhabitants of the area in front of a stream that they know is regularly polluted, but that on this last occasion seemed "of blood". The preliminary results of the analyses carried out by the Ministry of the Environment of the province of Buenos Aires have detected different "shades of red organic pigment (Acid Red), which allow to limit (the origin) to the industrial sectors that use the pigment in their production processes: tanneries, agri-food, textile, pharmaceutical".

Provincial authorities said in a press release Thursday that they were “inspecting all industrial plants that use this pigment” in the sector. Separate preliminary analyses also “excluded a priori the presence of cyanobacteria and potentially toxic bacteria,” the ministry added.