Abstract : Oyster farm structures represent artificial obstacles which can disturb tidal currents and wave propagation, and thus modify sediment transport patterns. Local deposition may result from these modifications, in proportions that may threaten the oyster farming. The impact of structures on hydrodynamics, waves and currents, is investigated at different spatial scales by means of in-situ measurements, experimental tests and numerical modeling. These different approaches show that in the near-field, tidal currents are modified in terms of intensity and direction but there is no significant impact on the waves. On the other hand, at the scale of the oyster farm, a significant reduction of the current velocities and a large wave height attenuation are recorded. From a sedimentary point of view, higher turbidity levels and a smoother evolution of the sediment altimetry are observed under an oyster table than in the adjacent alleys. The bottom shear stress reduction, due to wave attenuation by the farm, induces a decrease of the wave erosive potential, which leads to a different sediment granulometry and a deposition trend in the downstream part of the farm (with regards to wave propagation). A numerical sediment transport model of Mont saint-Michel Bay is used and calibrated by our in-situ measurements. It shows that the impact of structures on long term sedimentation is essentially local and is negligible at the scale of the bay.