Anotace:
In February 2022, the long-term pollution of the Slaná River by discharge of mine water began. The pollution is evident in a long stretch of the river, due to the bright orange colour of the water. According to media reports, there was significant damage to ichthyocenoses, despite the fact that no mass death of fish was recorded. About a month before the survey was carried out, the concentration of dissolved substances was reduced by approximately 80%. The goal of the ichthyological survey was to determine the current state of ichthyocenoses affected by pollution. The presence, abundance and age representation of individual species of fish and roundmouths at three locations were examined. A decrease in species diversity, low densities in relation to the character of the flow and a distorted age structure in the affected locations were found. The condition of ichthyocenoses improved in direct proportion to the distance from the point of discharge of mine waters. When comparing results of current ichthyological survey with previous surveys and based on the absence of other significant sources that could negatively impact river ecosystems, it is possible to consider this pollution of the Slaná River to be the reason for degradation of ichthyocenoses.