<p>This study is an initial approach to the investigation the fate and transport of neutrally buoyant particles released in the Gulfs of Patras and Corinth system, a semi-enclosed microtidal marine system in central Greece. Hydrodynamics and particle movement were numerically simulated using the MIKE 21/3 Flow Model FM Hydrodynamic (HD) and Particle Tracking (PT) modules. First, a 2D barotropic model was applied to simulate the transport of neutral particles driven only by tidal currents in the absence of wind. Results showed limited dispersion, with most particles remaining close to their release points, except in areas with strong tidal flows such as the Rio–Antirio Strait, central of the Gulf of Patras and the western part of the Gulf of Corinth. In the second case, a 3D model was implemented that included the combined action of tidal flow and river outflows. The 3D simulations suggest that particles released near river mouths were transported farther and followed more complex pathways, influenced by coastal circulation and river freshwater plumes. River outflows significantly modify circulation patterns, affecting the fate of neutrally buoyant particles in the system. Local hydrodynamic features and complex coastline geometry also play an important role. Areas of enhanced particle retention were indicated mainly in the northern Gulf of Corinth and the central to southern Gulf of Patras, while particles released near the Rio–Antirio Strait were rapidly exported toward the open Ionian Sea.</p>