Three days of diving in the mesoscaph Auguste-Piccard allowed us to observe and to photograph the morphology of the sedimentary deposits of the Léman between Meillerie and Nyon. Underwater landslides, paths and tracks of molluscs and fish were photographed. At a depth of 309 meters in the great plain, we found a structure formed of a succession of pits and humps caused by the interference of ripple marks made by various underwater currents. The origin of the latter is hypothetical.