The article analyses hydromorphological changes in the stream caused by the construction of beaver dams. For the period of three hydrological half-years, water level fluctuations, changes in water retention, and the diversity of the stream morphology were examined. The influence of atmospheric precipitation and beaver activity on water depth fluctuations and the amount of water retention was found. The average water depth before the dams was 69 cm and ranged from 29 to 97 cm. The average increase in water depth caused by the dams was 48 ± 18 cm. The water retention in the stream bed (pond capacity) ranged from 15.5 to 106.5 m3. The highest retention was recorded in August 2021 after heavy and long-lasting rainfall. The lowest retention was recorded in April 2022 due to the destruction of the D2 dam. Beaver activity also contributed to the transformation of the hydromorphological conditions of the stream. The Habitat Quality Assessment increased from 28 to 38 in places affected by beavers (an increase by 36%). The following changed: heterogeneity of the stream and riverbed material, diversity of vegetation types in the riverbed, diversity of elements accompanying woodland, and vegetation structure on the bank slopes. Extreme weather events and human activity have a significant impact on the functioning of beaver dams, which highlights their key importance in stabilizing water levels and protecting river ecosystems. The sensitivity of the river hydrological system to intense precipitation and its deficits highlights the need to protect natural channel structures that increase the retention capacity of dams and support the restoration of degraded areas by restoring natural hydrological and geomorphological processes.