Marine waters affected by eutrophication (Source: CMEMS)

The indicator shows the share of eutrophic marine waters in the Exclusive Economic Zone (EEZ). An area is classified as eutrophic if for more than 25 % of the observation days of a given year the chlorophyll concentrations as a proxy for eutrophication are above the 90th percentile of the 1998–2017 reference base line. Eutrophication is the process by which an excess of nutrients – mainly phosphorus and nitrogen – leads to increased growth of plant material, particularly algal blooms, in an aquatic body resulting in a decrease in water quality. This can, in turn, cause death by hypoxia of aquatic organisms. Anthropogenic activities, such as farming, agriculture, aquaculture, industry and sewage, are the main source of nutrient input in problem areas. The Marine Strategy Framework Directive (MSFD) requires Member States to report on eutrophication for their regional seas every 6 years. The Copernicus Marine Service has calculated the indicator from satellite imagery.