Changes in the composition and the structure of mollusc communities of the north part of Annecy Lake (Savoie, France) between the years 1929-1939 and the present period. -Between the years 1929-1939, mollusc communities of the north part of Annecy Lake were collected by Favre. After a study of his collection, malacological sampling were carried out in the same sites. A comparison of Favre's data with present data shows that: significant changes in the composition and the structure of the

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... ties occurred between these two periods; improvement effects of the physico-chemical quality due to the sewerage system construction, which began in 1961, were more efficient on the littoral zone communities than on those of the deep waters zone; several species colonized the Annecy lake, three of them Dreissena polymorpha, Pisidium moitessierianum and Potamopyrgus antipodarum being abundant in the north part of the lake. The recent arrival of P. moitessierianum, which normally only lives in large lakes of the plain and in the potamon of rivers, unlike the others Pisidium of Annecy, could be a result of the climatic change.