Storm surges are a hazardous phenomenon, since they may flood large coastal areas, causing socio-economical and habitation losses. Thus, the study of their characteristics and effects in coastal regions is crucial to prevent their negative consequences. This work aims at assessing the storm surges impact in the hydrodynamics of a tidal lagoon located in the north-western Portuguese coast (Ria de Aveiro). Storm surge amplitudes of 0.58 m, 0.84 m and 1.17 m for 2, 10 and 100 return periods, respectively, were determined adjusting the annual maximum amplitudes to a Generalized Extreme Value (GEV) distribution. To assess the hydrodynamic changes in the Ria de Aveiro under storm surge conditions, numerical modeling simulations were carried out, considering four scenarios: a single astronomical tidal forcing (reference) and astronomical tide plus 2, 10 and 100 years return period surges. Maximum levels and velocities for the entire lagoon and the tidal prism for the main cross-sections were determined and compared with the reference scenario. Generally, the model results suggest that during storm surge events the maximum levels increase in whole domain, with the largest increase found for the 100 return period storm surge scenario (1.17 m). The most significant changes occur at the main channels head for all scenarios, revealing that these regions are the most vulnerable to marginal flooding. Also, storm surges induce higher velocities and tidal prisms in the lagoon, increasing the marginal risk of erosion, as well as the salinization of the lagoon marginal lands.