Cyanobacteria alert on the Lez, the Méjean pond and the Salagou lake

Les interdictions prises concernent le Lez. ML – ML

Two dogs died in Pérols after drinking water. The bans (fishing, swimming, irrigation, etc.) due to this proliferation are numerous this summer in eastern Hérault. Overview.

Green algae are back! Naturally present in aquatic ecosystems, they proliferate especially in stagnant water due to an excessive supply of nutrients, particularly caused by high temperatures.

Two dogs died in Pérols

In Pérols, it is the eastern part of the pond, where swimming has been prohibited for almost two months, which is the most affected, the cyanobacteria being brought by a watercourse. At least two dogs died after drinking water from the Méjean pond this summer. The second was a Dalmatian who died during the night of August 15-16.

“We inform you that you must walk your dogs on a leash near the pond and especially not let them drink water from the pond”, warns the city of Pérols on its website. Confirming that "several dogs have presented serious digestive and neurological symptoms causing their death, after drinking water from the pond."

The municipality recalls “that due to the presence of high concentrations of cyanobacteria in the water of the Méjean Pond, the following are prohibited: swimming and any recreational activity involving exposure to the water of the Méjean Pond; consumption of fish caught; watering animals; watering market garden crops with water from the Étang du Méjean."

Bans taken on August 16 in Montpellier

In Montpellier, the presence of cyanobacteria is regularly observed in the Lez during the summer. This has been the case since August 16 and the publication of a municipal decree restricting the use of the Lez and its banks. The above-mentioned prohibitions therefore take effect today and run until the repeal of the order.

“Based on the results of biosensor analyses, the GEMAPI (Aquatic Environment Management and Flood Prevention) service of the Montpellier Metropolitan Area is warning of the presence of high concentrations of cyanobacteria in the water of the Lez, which could pose a risk to the health of those exposed.”

“Considering that current meteorological and hydrological conditions are conducive to the development of algae clumps on the surface of the watercourse, several bans are now in place in the Montpellier area: swimming, water sports, and eating fish fishing, watering animals, irrigating market garden crops with the waters of the Lez."

Ordered on July 19 in Lattes

In Lattes, the same prohibitions were taken on July 19 “on the Lez and its hydraulic system (roubines, canals…)”. This municipal order is not exceptional, since it is even recurrent during the summer period. In 2023, the various municipalities crossed by the river (Montpellier, Lattes, Castelnau-le-Lez, Prades-le-Lez) had taken municipal decrees from the beginning of July, following the heatwave at the end of June.

Red flag in Salagou

In Salagou, the vigilance threshold was reached at six sampling points out of nine, the Grand Site Salagou-Mourèze warned on August 13.“As a result, the Department has initiated the alert monitoring procedure. Signs have been installed all around the lake to inform visitors and warn of the potential risk. Further analyses are underway at a specialized laboratory."

"The presence of chlorophyll and cyanobacteria in the water is normal. The precautionary principle applies in the event of a risk of toxicity from this cyanobacteria. The emergency services in charge of the supervised beach of Clermont l’Hérault and the supervised beach of Vailhés have raised the red flag prohibiting swimming."

On August 20, the lake was kept on alert level 1, which "induces a potential risk of toxicity linked to the presence of cyanobacteria, it is not recommended to swim or ingest the water and dogs must be kept away from water."

"As a precautionary measure, the municipality of Celles has banned swimming in its municipality and that of Clermont l’Hérault within the supervised swimming area. The latest samples taken on Monday 19 August have been sent to the laboratory, which is currently carrying out an analysis to determine whether or not the cyanobacteria present in the lake are toxic."