Maps of sections of the Dyje, Rhine, Danube, and Morava rivers where we sampled round goby populations (green circles) on either side of river barriers (yellow rectangles). Estimates of population differentiation, FST, and the respective P-values (after applying a Benjamini-Hochberg correction for multiple comparisons within each river) are given for consecutive sampling sites along each river (white boxes), some of which are separated by a barrier (described in beige boxes with site name). Note that in the Danube, between Bergheim and Poikam, there are two other hydropower dams, each at Vohburg and Ingolstadt (with boat locks).