The Haringvlietdam, a large estuarine barrier, in the Netherlands recently implemented new sluice management allowing some inflow of saltwater during the high water period, so called ‘Kier’ management, to facilitate fish migration. The goal of this project is to determine fish passage success and movement before and after ‘Kier’ management and understanding their driving environmental factors, including the impacts of intensified searching patterns on the risk to be caught or predated. Besides, the gained knowledge will be used to optimize sluice gate operations and to investigate the consequences of improved management for upstream fish migration. Atlantic Salmon, Seatrout, Sea lamprey and North Sea houting will be tagged, including predation transmitters, to research fish movement patterns and passage behaviour at the Haringvlietdam and alternative entries at the Nieuwe Waterweg. The study will be conducted for 3 years and will assist in conservation and recovery of diadromous fish species and improve passage success at tidal barriers.