A healthy fish stock in the Dutch rivers, lakes and delta depends on good policy and management. This requires knowledge of ecology: how do natural processes and human interventions influence the freshwater ecosystem? Wageningen Marine Research studies the behaviour and habitat of fish species such as bream and eel and determines the size of fish stocks. We also study the impact of climate change and environmental development on freshwater fish. With this knowledge, we advise the government, commercial fishery and recreational fishery about developments and measures that benefit freshwater fish and biodiversity.