The Grevelingen estuary was dammed off and became a lake in 1971. Since 1978 a connection with the North Sea exists to keep the lake saline but management of sluic-es varied over time. Our research of several decades of monitoring data shows that water management lead to drastic changes in water quality and consequent eco-logical shifts in macrobenthic fauna. Benthic biomass, dominated by molluscs, showed major changes with an important role for invasive species. Implications are made towards future management to re-introduce mi-cro-tide (30-50 cm amplitude) in connection with the North Sea to improve water quality and the ecological status of the lake. As the reintroduction of tide will neg-atively affect terrestrial Natura 2000 habitats and spe-cies, including coastal breeding birds, the Dutch gov-ernment will mitigate and compensate for these effects.