Interreg Central Baltic CleanStormWater was an international project carried out in 2020-2022, aimed to improve the stormwater management around the Baltic sea. Stormwater management is becoming more and more relevant in our society due to factors like urbanisation and the increasing areas of surfaces impervious to rain water that urbanisation creates. Stormwater management may also become more relevant due to climate change and the potentially increasing volumes of annual rainfall. If left untreated stormwater can transport hazardous substances and environmental pollutants from urban environments into rivers, lakes and seas and thereby imposing a significant risk for the water quality and the ecosystem.