## 3 Results
### Serbian Water Quality Index (SWQI)
While existing parameters provide valuable insights into nutrient dynamics, oxygen conditions, and mineralization processes, the omission of coliform data and other microbiological indicators means that potential impacts on aquatic health and water usability remain uncertain. Overall, the available dataset suggests improvements in oxygen conditions and reductions in organic pollution over time; yet, increases in nitrogen and phosphorus concentrations highlight the need for continued monitoring to assess potential eutrophication risks. Incorporating microbiological analyses in future studies would ensure a more comprehensive evaluation of Ribnica Reservoir's water quality and its ecological integrity. Table 5 presents the average values of the measured water quality parameters based on two sampling events conducted in 2021, providing a more comprehensive representation of the annual conditions. In contrast, Table 6 displays the parameters obtained from a single sampling conducted in 2022, reflecting a snapshot of water quality for that year. All listed parameters have been incorporated into the calculation of the Serbian Water Quality Index (SWQI). \begin{table}
\begin{tabular}{c c c c c c c c c c c c c} \hline \hline
**Profile** & **A1** & **A1** & **A1** & **A1** & **A1** & **A1** & **A1** & **B1** & **B1** & **B1** & **B1** & **C1** \\ \hline Depth (cm) & 50 & 200 & 350 & 500 &  
The analysis of the Serbian Water Quality Index (SWQI) for the Ribnica Reservoir reveals a general improvement in water quality from 2021 to 2022. In the first year, values fluctuated between medium (82) and excellent (95) across different depths and profiles, with some variability indicating localized influences on water composition. The lowest SWQI recorded in 2021 was medium (82) at a depth of 450 cm in Profile B1, while the highest value of excellent (95) was observed at multiple depths, suggesting favorable conditions in specific zones. In contrast, the 2022 dataset shows an overall increase in SWQI values, ranging from good (89) to excellent (98), with notably higher readings across profiles and depths, demonstrating improved water quality parameters. The increase in SWQI scores between 2021 and 2022 suggests enhanced conditions in oxygen saturation, reduced biochemical oxygen demand, and more stable pH levels, contributing to an overall healthier aquatic environment. Oxygen saturation levels were notably higher in 2022, which aligns with the observed increase in SWQI across all profiles. Additionally, improvements in electroconductivity and nutrient concentrations may have reduced stress on the water system, contributing to the rise in water quality index values. The relatively consistent SWQI values across depths in 2022 indicate stronger water stability and potentially better mixing within the lake. While these trends suggest overall improvements, differences in scores at certain depths highlight the potential impact of external factors such as seasonal variations, anthropogenic influences, or shifts in nutrient dynamics. The profiles with consistently high SWQI values, such as those exceeding 95 (excellent) in 2022, could indicate areas with better circulation or lower contamination levels. However, deeper zones displaying slightly lower SWQI values--such as good (89) at 1000 cm and 1200 cm--suggest that some localized effects may still be influencing water quality at greater depths. The SWQI results emphasize the importance of continuous monitoring to assess long-term trends and potential ecological shifts. The observed SWQI values indicate that water quality in the Ribnica Reservoir was predominantly in the good category in 2021, with some profiles briefly reaching medium levels. In contrast, 2022 results show a clear improvement, with all recorded values falling within the excellent and upper good range, reinforcing the trend of enhanced water conditions (Table 7).