| Summary: | Abstract: The first impassable obstacles for the fish migration along the River Danube from the Black Sea are represented by the Iron Gates I and II hydroelectrical dams, constructed in 1972 and 1984 on 943 and 863 river kilometers, respectively. Construction of fish passages on these dams would make more than 800 river kilometers upstream reopened for fish migrations. The Iron Gates dams are jointly operated by Romania and Serbia and they represent the largest hydropower dam and reservoir system along the Danube River basin. Among migratory fish species affected by these dams are three critically endangered sturgeon species and Pontic shad (Alosa immaculata) as anadromous species, catadromous European eel (Anguilla anguilla) and more than 10 potamodromous fish species. Differences in time of upstream and downstream migrations have to be taken into account while considering the provision for free passage through the dams, as well as total lengths of upstream migrants, especially of species such as beluga sturgeon (Huso huso) that can reach total length of more than 3 m. Preliminary fish passage feasibility study could involve investigation of local hydraulic conditions at different discharges and operating conditions of dams, as well as investigation of fish behavior when they approach dams during migrations by fish tracking, telemetry, and Didson or Aris camera. Romania and Serbia could develop research teams for continual monitoring of fish behavior in the vicinity of dams, as well as in the reservoir between the two dams, based on the best experiences from other countries. Common work of biologists, ecologists, hydrologists and civil engineers is necessary regarding data collection, review of existing data, as well as for evaluation of the fish passage alternatives. Involvement of governmental agencies, local authorities, hydropower managers, researchers and NGO's from both countries is one of the prerequisites for successful completion of fish passages.
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