A model is developed by which the poison concentration due to a discharge of toxic matter in the coastal water is calculated. The outlet arises from a hypothetical accident to a ship loaded with dangerous materials. The oceanographic conditions are assumed to be mast unfavourable for a rapid dilution of the toxic matter and the current is assumed to be towards the coast. Calculations of the time development ,as well as calculetion is of areas constantly covered with :poison during a time·period of 45-55 hours are carried out for different conditions.