Development of measuring techniques enabled execution of detailed in situ measurements in the maritime part of the Vistula estuary. The data gathered were then used for verification of a three-dimensional model. In situ measurements of hydrodynamic conditions (magnitude and direction of water currents, salinity, temperature) were carried out in autumn 1995 as short-term and long-term registrations. Calculations done by the numerical model, based on collected hydro-meteorological data, agree well with short-term registrations. The influence of the forcing functions and numerical coefficients on the results of modelling are discussed.