Concept
The Étang de Thau (etɑ̃ də to; Estanh de Taur) or Bassin de Thau is the largest of a string of lagoons (étangs) that stretch along the French coast from the Rhône river to the foothills of the Pyrenees and the border to Spain in the Languedoc-Roussillon. Although it has a high salinity, it is considered the second largest lake in France. It is about long and 8 km wide, with an area of . The mean depth of the lagoon is , but in the central navigation channel it can be deep. Near Bouzigues is a deep depression with a diameter of . This 'Fosse de la Vise' is the source of a hot spring that feeds the spa in Balaruc. Its size and depth, which distinguish it from other lagoons of the region, is explained by the geomorphology of the region since the syncline formed by folding produced the corresponding anticline of the Gardiole in the north-east. Until relatively recently, the lagoons from Marseillan to the Rhône were a continuous stretch of inland waterway. Early settlers described this as "une petite mer intérieure et tranquille" ("a small sea, inner and quiet"). It provided access to, in particular, Marseillan — a fishing village that became a trade centre. Linked now by the Canal du Rhône à Sète to the river Rhône and by the Canal du Midi to Bordeaux via Toulouse, the lagoon also has access to the Mediterranean at Sète. There is also a small canal (le canal des Allemands or the pisse-saume) that links the western end to the sea at Marseillan Plage. This canal is only suitable for small craft since both road and railway bridges restrict height. To the east, between Balaruc and Sète, the borders of the lagoon are largely industrial. The south bank is formed by the coastal strip from Sète to Cap d'Agde. The northern side has villages dedicated to fishing and the production of shellfish. There are harbours in the towns of Marseillan, Mèze and Bouzigues, with smaller ports dedicated to shellfish on the northern shore. There is significant variation in the rainfall in the catchment basin for the lagoon, both seasonally and between years.
