Аннотация:A numerical simulation of 3-D passive tracer trajectories is used to study pollutants pathways in the Caspian Sea. We used the INMOM reanalysis data set representing the state of the Caspian Sea Hydrology to simulate trajectories. We found that upwelling featured to the eastern coast of the Middle Caspian is characterized by vertical particle movement with the order of hundredths mm/s. The vertical motion is modulated with a frequency close to the inertial one. As a result of the passive tracers’ trajectories analysis, the features of water exchange in the Middle and Southern Caspian Sea were found. Lagrangian particles move from the western part of the Middle Caspian along the bottom of the Apsheron sill towards the Southern Caspian, rise in the water column and cross the Apsheron sill, and then descend to the deeper layer