Abstract S'Ena Arrubia Lagoon (Central-Western Sardinia) is a eutrophic system and is strongly influenced by human activities. The sea mouth was widened in 2000 to reduce the high trophic levels and improve its hydrodynamics. To study the environmental consequences of this 'reframing', nutrient concentrations and phytoplankton were compared before (1990-1999) and after (2000-2003) the hydrological works. The land-ocean interactions in the coastal zone (LOICZ) biogeochemical model was also applied for some years during the previously mentioned two periods. Results showed significant variations for salinity, Chlorophyll a and phytoplanktonic principal classes, and the LOICZ model results indicated that the water residence time was less. However, the expected decrease of nutrient concentration was not observed. Sea-mouth widening is one of the possible management strategies that can be used to reduce the high trophic state of lagoons. It should, however, probably be used in conjunction with watershed management if the objective is also to reduce eutrophication.