Background . Species-specific feature of wild reindeer, Rangifer tarandus L. are large-scale migrations, including through rivers. We analyzed the patterns of animal behavior when overcoming a water barrier, which served as the basis for creating a simulation model. Materials and methods . Air-surveys and ground-based observations were carried out on the Verchniaya Taimyr River with coordinates 73°44´N, 96°45´E. Based on the results, ethograms of chrono-shoric trajectories and configurations of Rangifer tarandus L. were compiled when overcoming water obstacles, which were taken as a basis for constructing a mathematical model of group overcoming water obstacles with highlighting significant properties and characteristics. Results . The behavioral dominant during migration is movement, with strictly motivated nature and timing of migration (climate justification). Any water area along the route is an obstacle of natural origin, overcoming of which should support the given behavioral stereotype as much as possible, that is, minimize energy costs and time loss. When overcoming a water obstacle, the leader occupies an avant-garde position in the herd, usually he is an old female who follows migration paths, the use of which was successful in previous years and enshrined in the strategy of developing the territory of wild reindeer during the period of migration. For any herd structure, different biophysical indicators, the averaged characteristics and patterns of herd movement through the water area do not change, which is confirmed by the simulation model. Conclusions . The constant crossings across the water areas located on the migration paths have fixed certain patterns of movement in the wild reindeer, which is confirmed by the simulation model. The desire of animals to preserve the spatial configuration fixed when overcoming water barriers is one of the adaptive-population forms of wild reindeer, which can be considered as the result of the selection process, the only evolutionarily stable one selected among many strategies.