Figure 1

Sampling sites (2019) on the Danube River (1–29) and its tributaries (Inn-30, Morava-31, Vah-32, Hron-33, Ipel-34, Drava-35, Tisza-36, Sava-37, Velika-Morava-38, Timok-39, Iskar-40, Jantra-41, Russenski-Lom-42, Prut-43). Georeferenced data were taken from DanubeGIS (https://www.danubegis.org/) and topographic background from OpenTopoMap.