1. Vertikal Mixing [%] 2. Thermal Stratification [K] 3. Haline Stratification [psu] 4. Frontal Zone Index In the summers from 1981 to 1983, alarming oxygen deficiencies occurred in the bottom water of the German Bight. The hydrothermodynamic conditions during these periods of oxygen deficiency have been investigated with the model MACH3. Figures 1 - 4 show the weekly averaged results of the simulations for that week in August 1982, which lies in the midst of the oxygen deficiency period as detected by MACH3. For comparison, the observed oxygen deficiencies with oxygen saturations less than 40% are indicated by the red-edged areas. Oxygen deficiency is physically possible within the entire area, where vertical mixing does not occur at all (deep-blue area in figure 1). Actually however, the area of observed oxygen deficiency is essentially smaller. The area of observed oxygen deficiency is located entirely within the thermally stratified region (figure 2), but coincides far better with the haline stratified region (figure 3). Finally, the river plume front (deep-blue area in figure 4), which acts as the western barrier for the spreading of coastal waters, highlights that the observed oxygen deficiencies were caused directly (detritus) or indirectly (enhenced primary production by high nutrient influx) by oxygen depleting loads of River Elbe.