Eutrophication is one of the most common causes of water quality impairment of inland and marine waters.Its best-known manifestations are toxic cyanobacteria blooms in lakes and waterways and proliferations of greenmacro algae in coastal areas. The term eutrophication is used by both the scientific community and public policymakers,and therefore has a myriad of definitions. The introduction by the public authorities of regulations to limiteutrophication is a source of tension and debate on the activities identified as contributing or having contributeddecisively to these phenomena. Debates on the identification of the driving factors and risk levels of eutrophication,seeking to guide public policies, have led the ministries in charge of the environment and agriculture to ask for a jointscientific appraisal to be conducted on the subject. Four French research institutes were mandated to produce acritical scientific analysis on the latest knowledge of the causes, mechanisms, consequences and predictability ofeutrophication phenomena. This paper provides the methodology and the main findings of this two years exerciseinvolving 40 scientific experts.