In this paper we explore the role of the river run-off, the tidal regime and the local winds in the dynamics of the Ria de Arousa estuary during the summer period, using for that purpose the numerical model Delft3D. First of all, a simulation under real hydrological and meteorological conditions is conducted in order to validate the ability of the model to reproduce measured salinity and temperature profiles. Subsequently, a series of simulations considering simplified meteorological input data and river discharge conditions are carried out in order to study the sensitivity of stratification conditions in the estuary to the various external forcings of the model. The results are analyzed using potential energy anomaly arguments, which allow quantifying and ranking the contribution of the different processes to the stratification of the estuarine system.