The map shows the mean annual concentration of nitrates (NO3), expressed as milligrams of NO3-N per litre of water, observed in river monitoring stations and reported by EEA member countries via WISE. For most countries the mean annual value is based on observations over the whole year, whereas some countries only collect samples during the growing season (due to ice cover in winter).
Nitrates in excess can cause eutrophication in downstream coastal waters by stimulating excessive growth of algae and other aquatic plants (when nitrogen is the limiting factor for growth) and indirectly causing oxygen deficiency in the bottom waters and reduced biodiversity. High concentration of nitrates also represents a health risk in drinking water (the World Health Organization guideline for drinking water is less 10 mg NO3-N/L, which is the equivalent to approximately 50 mg NO3/L).
The purpose of the map is to provide an overview of the mean annual value of nitrates in rivers across Europe and to enable the user to compare values per country, River Basin District (RBD) or individual monitoring station, depending on the scale of visualisation. Historical data since 1993 can be displayed using the time slider.