This paper gives the physical oceanography background for the Bremerhaven Workshop on Biological Effects of Contaminants in the North Sea and the resulting papers contained in the volume. For the water quality bioassays, the benthic community analysis, and the benthic sediment bioassays the relevant hydrographic conditions are described and the results of model simulations carried out for the workshop are presented as well as an evaluation of the oceanographic observations carried out on board RV 'Valdivia' during the workshop. Two main conclusions must be drawn: (1) The German Bight is an area characterized by strong mesoscale variability in physical properties such as fronts, meanders and eddies. This vanabil~ty is also seen in the mobile superficial sediment and the resulting variability of the suspended matter content. (2) During the workshop the hydrographic situation in the German Bight was marked by highly saline inflows to the German Bight from the English Channel. The stations close to the East-Friesian coast are located within the contaminated Continental Coastal Water; the more offshore stations met more or less undiluted water originating from the English Channel, with a high portion of Atlantic Water.