France, July 19 -- A beach in Biarritz, in southwestern France, was closed to swimming on Thursday due to a high concentration of a toxic micro-algae, which had caused a wave of panic and the closure of several Basque coast beaches in 2021.

"If the presence of the micro-algae Ostreopsis had been observed for several days but at moderate levels, its sudden intensification was likely caused by the swell that occurred at the beginning of this week," stated the Regional Health Agency (ARS) and the Basque Country Agglomeration Community in a joint statement.

Several surfers and swimmers, in particular, reported to the authorities symptoms specific to the presence of this micro-algae, which is invisible to the naked eye, but "no reports of se...