Seasonal simulations of potential pollutant spreading from two major rivers, Soča (Isonzo) and Po were performed using the particle-tracking based model NAFTA3d. We show concentrations and adequate circulation fields for a few typical situations with elevated concentrations in different parts of the computational domain. Daily circulation fields for the entire year 2012 were obtained from the NAPOM model. Particles with different relative density were observed. The particles with negative buoyancy sank to the sea-bottom close to the river mouth. The particles with neutral buoyancy dispersed throughout the water column; elevated concentrations from the Soča river inflow occurred in the vicinity river mouth, while particles from the river Po spread towards the eastern coast of the Northern Adriatic. Buoyant particles from the Soča mostly spread with the general circulation in the Northern Adriatic: along the northern coast towards Venice and further south to the Po river mouth. In certain conditions the floating particles can concentrate in a slick with coordinates of the centre at 44° 55' S in 13° E. Buoyant particles from the Po spread towards south-east and further to the east. However, these simulations are less reliable because of the vicinity of the open boundary. Highest concentrations occur with floating particles which also move faster due to stronger currents at the sea surface.