The map depicts 25 European Ecoregions based on the ideas of Illies (1967) and adapted by the European Union to assess the ecological quality in European water bodies.
European Environment Agency (EEA WISE-WFD database) (link)
European Environmental Agency
The European Ecoregions for Rivers and Lakes shapefiles can be downloaded from the European Environment Agency:
https://www.eea.europa.eu/data-and-maps/data/ecoregions-for-rivers-and-lakes
