The Thau pond (illustration) -

N. Bonzom / Maxele Presse

Navigators, divers, fishermen and swimmers must avoid the Thau lagoon at all costs: a rare natural phenomenon of the reversal of currents between fresh and brackish water, called "inversac", is underway in the lagoon, near Sète .

This causes very dangerous siphon effects, warns the Hérault prefecture.

"In the absence of significant rains this fall, the aquifers of the Hérault department are experiencing a recharge deficit" in fresh water, explains the prefecture.

These low waters combined with an elevation of the level of the pond of about 30 cm, due to a sea surge, are most likely at the origin of the inversac, she adds.

Flooded houses

For several weeks, neighboring houses have been flooded by this phenomenon.

For example, a resident discovered 20 cm of water in his living room, told France Bleu Hérault on December 1.

“I discovered a river in my house,” he told the Hérault station.

The water came out through the floor of my yard, and through some walls in the living room.

I called the fire department, who set up seven pumps that have been running nonstop for forty-eight hours.

I've never seen that.

"

Video - A water source appears in the living room of a resident of #BalaruclesBains #inversac https://t.co/urSMyagZvI - via @francebleu

- Sébastien Garnier (@sebvlm) December 1, 2020

"For safety reasons, users of the lagoon (sailors, divers, fishermen, bathers, etc.) must avoid this sector", warn the authorities, who have published "an urgent notice to sailors", who no longer have the right to be there.

Researchers are mobilized to analyze and follow the evolution of the phenomenon which had not occurred since 2014 and "will probably last until the next rains", which would make it possible to recharge the groundwater tables with fresh water.

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