ABSTRACT : The Bosphorus tube tunnel, which is constructed under the Bosphorus strait by the immersed tunnel method, is under construction in Istanbul, Turkey. It is well known that the Bosporus strait has two-layer current system and its current situation changes rapidly. To keep quality and safety of installation of the tunnel elements, it is important to know the current situation in the immersion process before its practice. In this study, the current forecast system is developed to provide the current information required in the immersion process. The system consists of the water level forecast model and the current forecast model. The water level is forecasted from air pressure and wind, which are obtained from on-line monitoring and meteorological service. The current is forecasted from the water level, taking the density interface into consideration. The system is already under operation and it gives good current information for marine works.