The areas of highest species richness clearly coincide with the lower parts of the large rivers flowing to the Black and Caspian seas, such as Danube, Bug, Dniestr, Dniepr, Don, Volga and Ural. Eastern and central Europe are also particularly rich, as is all of the Balkan Peninsula, and the catchments of the Elbe and the southern Baltic Sea basin.
At 80%, the level of freshwater fish endemism within Europe is very high, so the overall distribution of European endemic species is similar to that of overall species richness at the European level. Many species are restricted to one, or very few, waterbodies. The most important hotspot of endemism in central Europe is the region of subalpine lakes in Austria, Germany, Switzerland and France. Another centre of freshwater fish endemism exists in northern Europe, in Iceland, Ireland, Scotland, Wales, Norway, Sweden, Finland and Russia. In the tributaries of the Mediterranean and the western Black Sea coast and Crimea, the species diversity per water body is low, whereas the rate of endemism is high. Many species occur in just one catchment, in few springs or streams, and about 60% of all freshwater fishes assessed as Critically Endangered in Europe occur in this area.
The distribution of threatened freshwater fishes in Europe shows divergent patterns from the picture of the overall species diversity.
The highest concentrations of threatened freshwater fish species are found; (1) along the northern Mediterranean coast, (2) on the tip of the Crimean Peninsula, and (3) in coastal streams of Bulgaria and European Turkey. All three regions have many locally endemic species, with natural ranges limited to one or few streams, springs or rivers. In certain areas within these regions, almost every river has its own unique freshwater fish fauna composed of local endemics.