Aim of the study:
Cyanobacterial blooms lead to an increase in organic matter and higher concentrations of Biochemical Oxygen Demand over 5 days (BOD5) and Chemical Oxygen Demand (permanganate method) (CODMn), simultaneously causing oxygen depletion. In addition, pH levels rise, which may adversely affect the functioning of the aquatic ecosystem. The aim of this study was to evaluate the effectiveness of the Water Quality Improving Installation (WQII) in reducing (nitrate nitrogen) NO3-N concentrations and changing the organic matter content and pH of the water separated by a fin boom in reservoir.

Material and methods:
Generalized linear models (GLMs) were applied for NO3-N, BOD5, and CODMn and pH.

Results and conclusions:
The results showed a statistically significant decrease in NO3-N level at the tap outlet compared with the pipeline inlet. For the remaining parameters (pH, BOD₅, CODₘₙ), no statistically significant differences were observed, although a favorable downward trend in values was noted at the outlet of the installation. Measurements of NO3-N reduction efficiency showed markedly higher effectiveness in water collected directly from the installation tap (median 70%) compared to samples from the reservoir (median 39.4%), suggesting partial mixing of water within the reservoir. The reduction of NO3-N and organic matter limits the availability of nutrients for phytoplankton and reduces oxygen consumption, contributing to ecosystem stabilization and the improvement of the ecological quality of the studied reservoir. The results confirm the effectiveness of the applied installation in improving water quality parameters and reducing the risk of eutrophication.