Anglet beach, located in the south of the French Atlantic coast, has been experiencing severe erosion for several decades, whereas recurrent dredging has been necessary to fight against the shoaling of the mouth of the Adour River. The channel entrance is protected from the very energetic wave climate by a main jetty, the effect of which on the system appears to be crucial. In this paper, we study the relationship between the two systems in terms of sedimentary exchanges. First, we determine the time history of volume of subtidal beach sand with a bathymetry dataset spanning 24 years. This analysis highlights continuous and large erosion affecting the subtidal part of Anglet beach. This phenomenon had been masked until 1990 thanks to dredged sand releases. However, after that date, the drastic reduction of artificial sediment intakes led to a drop in the sand volume. Numerical modeling is used to study the flow pattern around the mouth of the river. Different wave scenarios are simulated with the TOMAWAC spectral model. The flows induced by waves and tides are then computed with TELEMAC2D (EDF/DRD). The sheltering effect of the jetty on waves is found to generate cross-currents directed to the river mouth. The magnitude of these currents is strongly dependent on the wave class energy and sea level. Local sediment fluxes are then estimated at the limit between systems. This calculation shows that cross-currents induced by the three most energetic wave classes could be entirely responsible for the sediment motion from the coast of Anglet to the mouth of the Adour River.