Aim of the study:
The paper presents an assessment of the possibility of the hydraulic drop structure, which was partially destroyed, and the riverbed in the region of the structure is slowly renaturized. As a result of damage to the structure by natural processes, elements displaced from the structure were deposited in the energy dissipating pool and on the river bed downstream of the structure, limiting bed load transport as well as transport of wooden debris. These fluvial processes created a cascade-like structure that caused a change in the regime of water flow through the hydrotechnical structure that was not planned or designed originally.

Material and methods:
As a result of the partial destruction of the structure, the water flow regime was changed so much that it is possible to overcome the section of the river on which the drop structure was built by fish of various species, without the need to build additional devices. As a result of field measurements, six potential fish migration routes through the region of damaged structure were determined. Then each fish migration route was assessed from the point of view of the possibility for fish to pass the structure.

Results and conclusions:
The analysis showed that the partly damaged drop structure, creates favorable conditions for the migration of some fish species. It can be concluded that the elements detached from the drop structure and deposited in the downstream the structure should be not removed from the river, because they improve the environmental conditions for aquatic organisms in terms of their migration.