Summary:

In the recent decades, due to improper management of river ecosystems adverse effects occurred in riverbeds hydromorphology. Increased water retention and use of hydroelectric rivers, which entails the construction of new hydro power plants requires a new look at the continuity of the river corridor. According to the RDW "heavily modified water body means a body of sur-face water, the nature of which has been significantly altered as a result of physical alterations by human [...]"[Dyrektywa 2000/60/WE]. The heavily modified water bodies should aim to achieve good ecological potential of waters. It is to be achieved through the construction or reconstruction of water structures to ensure efficient migration and living conditions for fish and other aquatic organisms.The aim of this study is to determine the construction limits of rock fish-ladders that meet the biological criteria of fish in the Skawa river. Laboratory measurements were carried out on the physical model of rock fishladder. The re-sults of laboratory measurement were used to calculate hydraulic condition within fishladder to determine biological stability of fishes: discharge, velocity of water, water depth and energy dissipation.