The initial results of modelling of suspended matter (SPM) concentration are presented. The three-dimensional model proposed allows one to calculate the transport, erosion and deposi-tion of a mineral part of seston in the Gulf of Gdansk. The loads of SPM from rivers, atmosphere and the open sea, based on either real data or other model simulations, are included. In this model, the settling velocity of seston particles is assumed to be proportional to the Stokes' one computed for particles of 4 mm in diameter. Erosion and deposition rates depend on the bed shear velocity computed from hydrodynamic model. Results of computations corresponding to a period of one year are compared with in situ ob-servations carried out in the 1996 year and satellite data. In general, horizontal and vertical distri-butions of mineral SPM concentration computed from the model show a characteristic for this area pattern of water turbidity, however, quantitatively the results obtained are in rather poor accordance with real values.