## 3 Results
### Physicochemical Status  
The general physicochemical status at each research point is below good (class III). The parameters that worsen this status are EC, NO\({}_{2}\)-N, and PO\({}_{4}\)-P (class III, II, and II for individual parameters; Figure 2). The smallest exceedances of the norms [19] for the analyzed parameters occurred in the case of NH\({}_{4}\)-N, BOD\({}_{5}\), NO\({}_{2}\)-N, and NO\({}_{3}\)-N (respectively: 0.13, 0.21, 0.22 and 0.29), and the biggest occurred for EC, temperature, and DO (respectively: 1.00, 0.94, and 0.83). \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Parameter** & **Point** & **1 (Median \(\pm\) SD)** & **2 (Median \(\pm\) SD)** & **3 (Median \(\pm\) SD)** & **4 (Median \(\pm\) SD)** \\ \hline pH & \(8.00\pm 0.48\) & \(7.90\pm 0.50\) & \(8.00\pm 0.51\) & \(8.00\pm 0.45\) \\ \hline EC (\(\mu\)S/cm) & \(1087\pm 358\) & \(1103\pm 363\) & \(1103\pm 359\) & \(1082\pm 358\) \\ \hline Temp. (\({}^{\circ}\)C) & \(13.70\pm 7.59\) & \(13.80\pm 7.47\) & \(13.70\pm 7.48\) & \(13.70\pm 7.35\) \\ \hline Turb. (NTU) & \(3.70\pm 7.30\) & \(3.78\pm 9.44\) & \(3.70\pm 7.02\) & \(3.40\pm 7.13\) \\ \hline NH\({}_{4}\)-N (mg/L) & \(0.16\pm 0.17\) & \(0.15\pm 0.17\) & \(0.14\pm 0.17\) & \(0.14\pm 0.16\) \\ \hline NO\({}_{3}\)-N (mg/L) & \(1.33\pm 0.91\) & \(1.70\pm 0.92\) & \(1.57\pm 0.93\) & \(1.40\pm 0.93\) \\ \hline NO\({}_{2}\)-N (mg/L) & \(0.026\pm 0.019\) & \(0.024\pm 0.019\) & \(0.021\pm 0.020\) & \(0.021\pm 0.019\) \\ \hline PO\({}_{4}\)-P (mg/L) & \(0.090\pm 0.037\) & \(0.085\pm 0.037\) & \(0.080\pm 0.039\) & \(0.085\pm 0.036\) \\ \hline DO (mg/L) & \(9.20\pm 1.89\) & \(9.10\pm 1.83\) & \(8.85\pm 2.09\) & \(9.00\pm 1.90\) \\ \hline BOD\({}_{5}\) (mg/L) & \(2.50\pm 2.19\) & \(2.45\pm 1.85\) & \(2.70\pm 1.72\) & \(2.80\pm 2.67\) \\ \hline \end{tabular} Designations in the table: SD—standard deviation.  
\end{table} 
Table 7: Descriptive statistics at analyzed research points. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Test Statistics** & \multicolumn{2}{c}{**Point 1/2**} & \multicolumn{2}{c}{**Point 3/4**} \\ \cline{2-5}
**Parameter** & **Z** & **\(p\)** & **Z** & **\(p\)** \\ \hline pH & \(-1.118\) & \(0.264\) & \(-2.138\) & \(0.033\) * \\ \hline EC & \(-2.763\) & \(0.006\) * & \(-1.890\) & \(0.059\) \\ \hline Temperature & \(-0.989\) & \(0.323\) & \(-1.598\) & \(0.110\) \\ \hline Turbidity & \(-0.009\) & \(0.993\) & \(-0.721\) & \(0.471\) \\ \hline NH\({}_{4}\)-N & \(-1.580\) & \(0.114\) & \(-0.055\) & \(0.956\) \\ \hline NO\({}_{3}\)-N & \(-1.304\) & \(0.192\) & \(-1.753\) & \(0.080\) \\ \hline NO\({}_{2}\)-N & \(-0.317 By analyzing the differences between the results of upstream and downstream hydropower plants, the physicochemical status is improved for BOD\({}_{5}\), DO, PO\({}_{4}\)-P, and EC (by: 6.19%, 3.85%, 3.31%, and 0.52%, respectively) and worsened for pH and NO\({}_{3}\)-N (by 2.63% and 1.83%). It should be noted that the Wroclaw I hydropower plant improved the physicochemical status for seven out of nine assessed parameters (from 1.03% to 7.41%). In two cases, no changes were noted. The Wroclaw II hydropower plant improved its status in two out of nine cases (from 5.13% to 7.41%), worsened in three out of nine cases (1.33% to 7.55%), and in four out of nine cases, there was no difference between the results. When analyzing all the results of the average physicochemical status obtained for the parameters upstream and downstream of the Wroclaw I and II hydropower plant (Table 9), it can be seen that in most cases, there were no changes in the average physicochemical state after passing through hydropower plants (Wroclaw II hydropower plant--from 72.22% to 100%; Wroclaw I hydropower plant--from 63.89% to 100.00%).