Between 1960 and 1980, the trophic state of Lake Geneva (situated between France and Switzerland) has changed from oligotrophic to eutrophic. Since then, the areal hypolimnetic oxygen demand of 1.31 gm-2 d-1 is now the highest measured in Switzerland and low oxygen contents of less than 4 mg l-1 regularly occur in the deepest parts (300m deep). Oxygen depletion is to a large amount driven by sediment oxygen uptake (SOU). In a large and complex lake like Lake Geneva, SOU can vary significantly temporally and spatially and is strongly dependent on the diffusive boundary layer (DBL) thickness which in turn varies with bottom boundary layer (BBL) currents.