Étang de Berre, Saltwater lagoon in Bouches-du-Rhône, France

The Étang de Berre is a brackish Mediterranean lagoon about 25 km north-west of Marseille, in Bouches-du-Rhône. Its 155 km² make it France's largest lagoon and the country's second-largest natural body of water after the French part of Lake Geneva. It consists of the main basin, the Étang de Vaïne to the east and the Étang de Bolmon to the south-east, the latter separated from the main lagoon by the Jaï dune belt.

The lagoon's ancient name was Stagnum Mastromela, recorded by Pliny the Elder in Book III of his Natural History. The Canal de Caronte, its open-air link to the Mediterranean toward Port-de-Bouc, was later cut through, while the Canal de Marseille au Rhône reached L'Estaque via the Rove Tunnel. That tunnel has been closed since 1963, when a section of it collapsed.

The lagoon's Occitan name, estanh de Bèrra or mar de Bèrra, survives in Provençal usage. Pliny the Elder recorded its ancient name as Stagnum Mastromela. Around its 80 km of shoreline, 16 beaches are monitored for bathing-water quality, and the GR 2013 long-distance footpath follows part of the perimeter.

Ten communes border the lagoon, each offering different access points where visitors can walk along the shore and observe water activities. Having a car makes it easier to explore different sections and find the best vantage points.

The Marseille Provence Airport runway extends into the lagoon on reclaimed land. The ancient name of the Étang de Berre was Stagnum Mastromela, as recorded by Pliny the Elder in his Natural History (Book III).