The Lower Bug region is the habitat of the Eurasian otter (Lutra lutra¬), which, relying on channel reservoirs as reserves, also exploits the seasonal and permanent resources of small steppe rivers. With the climate-driven decrease in surface runoff, small rivers have become subject to complete or partial drying up, making it difficult for semi-aquatic mammals to live. The survival of the otter in the Southern Steppe is ensured by its use of the static and foraging potential of channel reservoirs and ponds. The latter are the key sites that serve as permanent and off-season reserves for the species, ensuring the survival and sustainable existence of otters in the small river network. The habitat specificity of the otter's sustainable habitats covers areas with different spatial and landscape characteristics, and hydrological, and foraging features, which allows us to distinguish three ecologically and ethologically distinct forms of the species. The first is the primary riverine form, represented by animals inhabiting the Southern Bug, Syniukha, and Ingul rivers, the second is the lyman-estuarine form, and the third is the river-pond form associated with small rivers. The current number of otters in the Lower Pobuzhzhia is estimated at 86–108 individuals, which is 38.5% more than in 2000–2005 and 58.1% more than in 1992–1995. The average breeding density is 0.489 individuals/10 ha of water area (excluding the coastal and marine zone). In some habitats, the local density of otters ranges from 0.181 (Berezansky estuary) to 1.14 individuals/10 ha (lower reaches of the Syniukha River, Kovalivsky plains). At the same time, the main reserves of the species generally remain unchanged—the channel-floodplain habitats of the Southern Bug, Ingul, and Ingulets, from which the animals disperse to the tributaries of these rivers and adult males migrate through local watersheds. Some small otter habitats are associated with the peaks and banks of the Tiligul and Berezan estuaries. The least studied was and remains the Ingulets centre of existence of the species, which was significantly affected by the consequences of hostilities.

The article presents the results of two-year ecological, hydrological and hydrochemical studies of Berezan, one of the steppe rivers of Mykolaiv region, which begins the Berezan estuary in the lower part of the Tyligulo-Buzka confluence. The current state of the Berezan River is characterized by a significant level of anthropogenic transformation of the watercourse associated with the construction of cascade ponds. The independent existence of the flow rate and yearround water content of the Berezan River without its support by technical means of water supply is impossible. According to the hydrochemical composition of the river water, it belongs to the bicarbonate-calcium type with a high content of sulfates, chlorides, and sodium, differing in an extremely dynamic level of mineralization — from 760 mg/dm3 during the flood to 2900 mg/dm3 during the low tide. No less active influence on the state of this small steppe river and the Berezan estuary initiated by it are also exerted by natural factors such as increasing aridity of the climate, transgressive tendencies of the Black Sea, increasing environmental temperatures, increasing evaporation volumes and changes in the balance of surface-underground water exchange. Because of this, the Berezan River today is no longer able to independently maintain the water content, flowability and stability of the hydrochemical regime, showing a tendency to transform into a seasonally draining network of streams. The current nature of the water filling of the river is ensured by a cascade of reservoirs and maintenance of the flow rate due to water discharges from the South-Bug irrigation system fed from the South Bug. Despite the hydro-ecological problems, the river is still an important draining watercourse of the Tiligulo-Buzka interfluve, providing drainage, water regulation of the area and replenishment of underground horizons, with which the drinking water supply of 19 settlements is connected.