The Manila clam Ruditapes philippinarum (Adams & Reeve, 1850) is one of the most commercially exploited bivalve in the world (Dang et al. 2010). Since 2013, it has expand-ed into Berre lagoon. In 2017, the density was between 41 and 1,264 clams.m–2, higher than that of other French sites (Mahé 2017, Sanchez et al. 2014). In February 2018, the professional clam fishery opened in the Berre lagoon. Starting in July 2018, an ecological crisis occurred and the clam stock was decimated (Mayot et al. 2020). Consequently, the fishery was closed. Following this event, the impact assessment was initiated with a clam stock study in spring 2019. During this campaign, 238 stations were sampled where the number and the size of R. philippinarum were assessed. To explain the clam distribution into Berre lagoon in relation to environmental conditions, hydrological condition and grain size were analyzed. These parameters are well known to control clam expansion (Le Treut 1986) and are believed to lead the clam distribution. Preliminary results show a total abundance of 552.07 million clams. No clear correlation was found between the hydrological condition, sedimentary data and the clams’ distribution at a large scale into Berre lagoon.