(a) PCA for 18 environmental parameters and 46 sites (sites DR4 and DR7 in the middle of second and third reservoirs were excluded). (b) Canonical correspondence analysis (CCA) triplot for 46 sites with different symbols and colours according to their positions at seven rivers sections (including two reservoirs), with 14 species (species abbreviation in orange: 11 NIMS-ObesObes: Obesogammarus obesus, ChelRobs: Chelicorophium robustum), other NIMS names abbreviations in text of Section 3.1; 3 native amphipods − GammFoss: Gammarus fossarum, GammRoe: Gammarus roeselii, SynrAmbl: Synurella ambulans) and 12 environmental factors as vectors.