The aim of the study was to determine the capacity of a selected section of the Sanna river, designated below the lower site of the weir in Zaklików. The capacity calculations included the conditions of flood water discharge, i.e. the reliable flow and the control flow, determined in accordance with the Regulation of the Minister of the Environment on technical conditions that should be ensured for the hydrotechnical structures and their locations. The paper presents the consequences of changes in the regulations regarding the determination of building type, for which reliable flow and control discharges are determined. These modifications in the regulations have an impact on changes in the determination of the probability value for water discharges related to the analysed weir. The calculation of the capacity of the tested section also took into account its technical condition, specifying the variant of calculations for the lack of maintenance works, i.e. for the current state and for the state after maintenance works, consisting in mowing vegetation on slopes and shaping the surface of river bottom, removing pits and shallows. The results of the calculations of capacity of the measured cross-sections showed that the performance of maintenance works will convey the flow of a Q3% reliable flow in the Sanna river, while the Q1% control flow will not fit into the riverbed and will cause inundation of the adjacent areas.