The overall objective of this study, implemented within the framework of EU's Green Infrastructure policy and the Blueprint to Safeguard European Waters, was to provide a solid methodological and quantitative basis for identifying the financial needs and policy implications at the EU level for natural water retention measures. These measures aim to work with nature's capacity to prevent floods by using ecosystem-based approaches and at the same time provide ecosystem services. STELLA has estimated the costs and benefits, and the potential of natural water retention measures for increasing resilience to climate change. We also analysed the potential of EU policy and funding instruments to promote no-regret measures. STELLA's team included a Water and Climate Change Expert, a Hydraulic Engineer, a Watershed Management Expert, a Sanitary Engineer, a Cost Benefit Analysis Expert, an Environmental Economist, an Environmental Engineer, and a Water Management Expert.