Harbor siltation is a problem that will exist as long as harbors exist and it is intrinsically linked to their primary function: providing 6 shelter for anchorage and operative conditions for loading and unloading ships. In these semienclosed basins, flow characteristics are one of 7 the main factors influencing siltation and water quality. One of the largest recreational ports of Europe, La Rochelle Marina (southwestern 8 France), is not spared by siltation, which requires serious dredging operations during a major part of the year. In this context, a three-9 dimensional model (5 TELEMAC-3D) has been used to investigate its hydrodynamics. Using a simplified approach, floating structures were 10 implemented in the model. Comparison with observations has demonstrated the need to consider these structures in our study. They sig-11 nificantly reduce velocity in the inner parts of the marina and concentrate current on access channels. Numerical results also highlight the joint 12 role of the macrotidal regime and wind stress in the movement of water masses and their residual circulation.