Abstract: The “Afsluitdijk” is an icon in the Netherlands. It is the 32 km long closure barrier, which separates the nature of the tidal Wadden Sea from the fresh IJssel lake. It was built for safety and economic developments between 1927 and 1932. Fish like salmon, eel and smelt, have great trouble in passing the remaining discharge gates near Den Oever and Kornwerderzand. The “FishMigrationRiver (FMR) Afsluitdijk” is a unique project near Kornwerderzand, allowing a variety of fish to reach their spawn, bread and living grounds. The FMR creates an intertidal zone, where fresh and saline water meet and fish might migrate, without jeopardizing the safety or increasing the salinity on the IJssel lake. Call it a barrier for water and salt, but open for fish almost continuously. An important step for the evaluation of the functioning of the FMR is the hydraulic operability. A series of hydrodynamic investigations was carried out to evaluate the various aspects of the FMR. They concern, the water exchange, the salinity, the velocities, the morphology and of course the behaviour of the fish.This presentation focus is on the hydraulic functioning of the FMR. Other presentations in this session focus on the ecological part of the FMR.