Tidal currents represent a promising energy source for electrical supply in Europe; however, nowadays there still exist important aspects to address regarding their exploitation prior to becoming a fully-fledged renewable energy. The accurate assessment of the available resource and the development of TECs (Tidal Energy Converters) are challenges which have been partially solved, but it is necessary to go further in the investigation of other aspects such as the impacts on the estuarine circulation. In this work, the impacts caused on the estuarine circulation in Ria de Ortigueira by the operation of two different tidal stream plants, one composed of floating and the other of bottom-fixed TSTs (Tidal Stream Turbines), were analysed by means of a three-dimensional model. Prior to using the model for assessing the impacts, it was validated based on field data at two measuring stations. Then, the tidal farms were implemented in the model as a momentum sink. The results show that there are no significant differences between the impacts caused on the general circulation by floating and bottom-fixed TSTs with slight reductions of the flow being apparent up to some km away the plant. Then again, strong differences were found in the vicinity of the plant.