The studies were conducted in the summers of 2017 and 2018 on three watercourses in Central and North-Western Poland where maintenance works involving disposal of sediment and silt were performed in the autumn of 2017. Monitoring of the ichthyofauna in the Rurzyca River and the Tywa River before (year 2017) and after the maintenance works (year 2018) indicated a decrease in the number of species. Altogether, 23 fish species were caught in all the watercourses. 12 species were not recorded after the studied rivers had been dredged. A slight decrease in the number of fish species was observed in each studied river after the maintenance works. Values of physicochemical parameters obtained for each watercourse indicate a low quality of their waters. After silt had been removed from the watercourses, lower N-NO3- values were observed at most research sites whereas N-NH4+ values increased significantly (except for one site on the Kanał Habdziński). Also, high volumes of P-PO43- were observed (except for sites 2 and 3 on the Kanał Habdziński and site 2 on the Rurzyca River). Maintenance works on small watercourses have a negative impact on the quality of waters and a less significant impact on the number of fish and biodiversity. This appears to be connected with migration of fish in the river during maintenance works and avoidance of the consequent unfavourable conditions to gradually return to their habitats afterwards.