Summer water temperature of lowland Mazovian rivers in the context of fisheries management

Abstract Water temperatures in three upstream and three downstream profiles of the Jeziorka, Świder, and Utrata rivers were recorded in the summer period of hydrological year 2015 using digital data loggers. The measurement data was used to estimate statistical and ecological thermal parameters. The results demonstrated that water temperature in the studied lowland rivers was quite similar, except in the downstream reaches of the Utrata River, which is subjected to strong anthropogenic modification. The best thermal conditions for the survival and growth of the cold-water fish assemblage were observed upstream in the Jeziorka River in Głuchów, while the worst were downstream in the Utrata River in Nowy Łuszczewek. However, the results suggest that in quasi-natural rivers, such as the Jeziorka and Świder, cold-water fish can exist and be stocked in both the upstream and downstream segments. For the warm-water fish assemblage, the best thermal conditions were noted downstream in the Utrata River, while the worst were upstream in the Świder River; nevertheless, differences between the rivers were relatively small. The results of the analysis have practical implications for managing these waters with a view to optimizing angling and natural resources.