With 750 producers, 2750 tables for breeding, 13 000 tons of oysters and 2 500 tons of mussels marketed every year, the shellfish production of the Thau lagoon represents at least 10 % of the national French production and a direct turnover of 33 millions € (Rey Valette, 2004). The Thau lagoon is a semi-enclosed coastal system sensitive to faecal inputs from the watershed (280 km2). In June 2004, the Autorithies classified the Thau lagoon as a « class B » area, from which live bivalve molluscs can be marketed for human consumption only after depuration. Until then, shellfish used to be collected for direct human consumption. The sanitary monitoring of the Thau lagoon shellfish growing area is conducted by the Ifremer french microbiological monitoring network for shellfish harvesting areas (Remi). The aim of the sudy is to determine the evolution of microbiological quality of the Thau lagoon’s shellfish and the impact of meteorogical conditions, with an analysis of Remi data collected during a 10 years period.