We present an assessment of the water mass dynamics in a reanalysis of the Mediterranean Sea with a focus on the Western basin. We use a θ-S based algorithm to compute the fractions of the main western Mediterranean water masses : Atlantic and modified Atlantic Waters (AW, mAW), Western and Levantine Intermediate Waters (WIW and LIW)and Western Mediterranean Deep Waters (WDW). The reanalysis retains the known mean characteristics of the water masses, their seasonal to interannual variability and main circulation patterns when compared with the literature. The imprints of winter mixing is particularly obvious with coherent variations of water mass volumes, mainly the yearly creation of WIW from mAW on northernmost shelves and of WMDW from all surface and intermediate layers during years of deep water formation. The results also highlight some unrealistic events of variability of the WMDW volume that are likely due to the data assimilation process. Re-computing the water mass volumes and transports without these altered years allowed to highlight the possible disruption of the large-scale barotropic cyclonic circulation in the Eastern Algerian basin in response to major DWF events over the Gulf of Lion. The reanalysis also showsan overtopping ofWMDW in the Sardinia Channel in 2009 leading to a major backward flow of mAW from the Tyrrhenian to the Algero-Provençal basin. Both processes affects the circulations of AW and mAW over the whole western Mediterranean.