The essential element of presented research is a description of the changes induced in the aquatic system as a result of human intervention by building barrage. The main objective of this study is to determine the differences in the quantity and condition of fish at the upper and lower station of the reservoir with regard to infected fish with Posthodiplostomum cuticola. Overall assessment of the species composition of fish at the upper and lower station of the reservoir in Brzeg Dolny allowed the quantitative analysis of fish in the Odra River. In the relevant section of the watercourse, the biggest fish of the carp family originated e.g. 89% of the total population. The study determines the overall health condition of fish at the lower and upper station. Particular attention was paid to changes in shell fish caused by vermines such as worm (Posthodiplostomum cuticola). Preliminary analysis, testing and a review of the literature data show the heterogeneous nature of the river ecosystem above and below grade on the Brzeg Dolny Reservoir. The barrage is an obstacle in the river which forms two separate living environments for fish, due to a significant difficulty in migrating between the upper and lower station, ...
