The Monitoring Programme covered the area of influence of the big dam located in the mouth of the River Tua (AHFT) as well as the upstream area on the river Tua and its main tributaries (rivers Rabaçal, Tuela and Tinhela). The objectives were to establish the diagnosis of freshwater mussel communities and to improve the knowledge of their population dynamics in order to assess the impact of the dam and the effectiveness of mitigation measures and to identify the other measures to minimize impacts associated with AHFT. This monitoring program was also designed to obtain information related with the success of compensatory measures proposed in the MC12n. The proposed monitoring program was made taking into account the following target species: Margaritifera margaritifera, Anodonta anatina, Potomida littoralis and Unio delphinus – since they have a higher conservation value and are one of the most affected faunistic group by the construction and operation of AHFT.