(A) Map of sampling locations (Odra-1, Šuma Žutica-2, Kraljica-3, Gromiželj-4, Bakreni Batar-5, Kraljevac-6, Lugomir-7). The Sava River system is delineated with a thick, black solid line, while the borders between countries are shown with thin, red dotted lines. (B) Distribution of Umbra krameri in Europe according to Wanzenböck (2004). (C) Detailed map of the lower Kupa River system. (D) Detailed map of the lower Matura River system.