Dams, weirs and other obstacles in rivers and streams represent interruptions to the longitudinal continuity of water courses, contributing to the reduction of population numbers of migratory fish species. In extreme situations, these disturbances may be responsible for the regional extinction of species more sensitive to fluvial hydromorphological changes. Pollution, habitat destruction and overfishing also contribute to this situation. However, in view of the diversity of uses associated with the different hydraulic infrastructures present in our rivers (like water supply, irrigation, flood protection, energy production, recreation and leisure, among others), it is of paramount importance to promote and achieve the compatibility of these activities with local and regional socio-economic impact, with the objectives of maintaining and recovering aquatic ecosystems.
Loss of longitudinal continuity in river ecosystems may be especially detrimental to diadromous species, by decreasing the habitat available to migratory fish or by blocking access to breeding (anadromous species) or growth (catadromous) habitats, preventing fish from completing their life cycle.