The French Atlantic coast hosts numerous macrotidal and turbid estuaries that flow into the Bay of Biscay that are natural corridors for migratory fishes. The two best known are those of the Gironde and the Loire. However, there are also a dozen estuaries set geographically among them, of a smaller scale. The physico-chemical quality of estuarine waters is a necessary support element for biological life and determines the distribution of species, on which many ecosystem services (e.g. professional or recreational fishing) depend. With rising temperatures and water levels, declining precipitation and population growth projected for the New Aquitaine region by 2030, the question of how the quality and ecological status of estuarine waters will evolve becomes increasingly critical. The MAGEST (Mesures Automatisées pour l’observation et la Gestion des ESTuaires nord aquitains) high-frequency monitoring of key physico-chemical parameters was first developed in the Gironde estuary in 2004 ; the Seudre and Charente estuaries were instrumented late 2020. First based on real-time automated systems, MAGEST is now equipped by autonomous multiparameter sensors. Depending of the stations, an optode is also deployed to secure dissolved oxygen measurement. By the end of 2020, MAGEST had 12 instrumented sites.

Portets is a measuring station located in the upper Gironde estuary (Garonne subestuary, about 20 km upstream of the Bordeaux metropolis.