Abstract The ability of small mammals to overcome water barriers in the forest zone was studied on the western macro slope of the Northern Urals in the upper reaches of Ilych River (which is 80 m wide). In August 2013–2020, counting was performed using traps set on rafts 15–25 m off the bank. In total 100 specimens of small mammals representing ten species were captured. An almost the entire set of small mammals of the region was thus found to reach the rafts, with the exception of a few rare species. Quantitative characteristics of the local populations were obtained and compared with their abundance levels on the open banks and under the forest canopy. The numbers of small mammals on rafts averaged 11.3 individuals per kilometer of the riverbank per day. The numbers of animals that crossed water barriers depended on the general abundance of nonresident animals in the populations. In different species, water avoidance varied, leading to changes in the species compositions on water and on the banks. The risks associated with traversing the water barriers are discussed. Even large rivers are shown to be traversable, and the ability of small mammals to overcome water barriers can support an effective exchange of individuals between the banks.
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