Surface water ecological status

Ecological Status assessments are performed by all EU Member States every 6 years, in 2009, 2015, and 2021. On the scale of Europe, around 40% of the surface water bodies are in good or high ecological status, with lakes and coastal waters having better status than rivers and transitional waters. The overall ecological status has not improved since 2009 but it has improved for some biological quality elements between 2009 and 2015. The results of the 2021 assessments are not yet known.

The ecological status for a water body is determined according to the 'one out, all out' principle. This principle implies that a water body can only achieve good status if all biological and supporting quality elements are assessed at least as good. In other words, the quality element with the worst status determines the overall status.

Water bodies in moderate, poor or bad ecological status require mitigation and restoration to achieve the good status objective. To plan such measures, the pressures that prevent water bodies from achieving good ecological status must be identified. These pressures include point sources of pollution, diffuse sources of pollution, water abstraction, and hydrological and morphological alterations. Types of impacts include nutrients, organic and chemical pollution, altered habitats and acidification.

The spatial distribution of ecological status is shown on the map below. The blue areas show where more than half of water bodies are in good ecological status. These are found in the northern countries, particularly the northern Scandinavian region and Scotland, as well as Estonia, Romania, Slovakia and in the Mediterranean region. In contrast, red areas show where less than half of water bodies achieve good ecological status. These tend to be found in central Europe.