This cluster of papers focuses on the phenomenon of eutrophication in freshwater and coastal marine ecosystems, particularly its role in promoting harmful algal blooms dominated by cyanobacteria. The papers discuss the links between eutrophication, climate change, nutrient control, and the management of lakes and reservoirs to mitigate the impacts of harmful algal blooms. Additionally, they explore the ecological and health implications of toxins produced by cyanobacteria in the context of eutrophication.