Source sous-marine de la Vise

The Source functions as a freshwater exsurgence of the surrounding karstic aquifer that discharges into the brackish water of the Étang de Thau.

When certain conditions are met, an inversac phenomenon occurs: the water of the Étang de Thau flows back into the aquifer, causing salinization of the groundwater table. In order to measure this phenomenon and its impacts, the BRGM of France and the University of Neuchâtel in Switzerland installed measuring instruments at the Source.

To prevent this phenomenon, a valve system was installed in July 2025 at the Source: when the pressure of the brackish water increases to the point of triggering an inversac, a valve closes the device, preventing salt water from entering the aquifer. This unprecedented installation is being monitored for three years before possibly being installed at other similar sites.

Sources:
* Article "Source de la Vise" from the collaborative encyclopedia Wikipédia en français: https://fr.wikipedia.org/wiki/Source_de_la_Vise
* BRGM, "L’inversac de Thau expliqué : des perspectives pour une meilleure gestion", 26 August 2025: https://www.brgm.fr/fr/actualite/actualite/inversac-thau-explique-perspectives-meilleure-gestion
* LHB Hydroscience Journal, "Suivi hydrologique de la source sous-marine de la Vise : questions techniques et scientifiques": https://www.tandfonline.com/doi/full/10.1080/27678490.2026.2664592#d1e364