# Change in Water Quality of the Vistula River During the Emergency Discharge of Untreated Wastewater
## 4 Conclusions  
As a result of the failure, some areas were contaminated with raw municipal wastewater, i.e., a mixture of domestic and industrial wastewater from office buildings, hospitals, and various enterprises, which may also contain heavy metals, detergents, and various substances. The amount of sewage load and its exposure time may impact the places where birds or fish (protected areas) occur. As a result of the discharge, pools were formed with a large number of nutrients. Based on the conducted research, the presence of surface water contamination was found in stations S3 and S4. These stations are located 300 and 500 m from the place of untreated sewage discharge and are situated on the left bank of the river. However, no pollution was found at stations S5 and S6, located 500 m from the collector, in the middle, and on the right part of the river bed. Based on the direct observations, the presence of pollution pools was found at a distance of 1200 m from the failure point (Figure 5). This study confirms that the discharged pollutants strongly deteriorated surface water quality. The presented paper provides valuable information on the extent of the impact of untreated municipal wastewater on the water quality indices. The concentration of N-NH4\({}^{+}\) in the mixing zone exceeded the limit of good water status established for the Vistula by sixfold (3.1 versus 0.5 mg\(\cdot\)L\({}^{-1}\)). In the mixing zone, the water did not meet the standard of good ecological status regarding the concentration of other nutrients, i.e., TN, TP, P-PO4\({}^{3+}\), and N-NO3\({}^{-}\) (twofold). Moreover, the high pollution levels expressed as EC, Cl\({}^{-}\), and SS were mainly caused by floodwater runoff from urban areas. Elevated phosphorus and nitrogen loads can contribute to the intensified eutrophication of aquatic environments. Furthermore, the consumption of drinking water with high concentrations of ammonia and nitrites may be associated with an increased risk to human health. As a result of the failure of the sewage system and the related pollution of the water environment, the managers took corrective actions. To prevent failure in the future, the transmission system was modernized, sewage transmission control was implemented, and the water quality in the river was monitored. Figure 5: Water pollution in the river (S1–S8—research stations). **Author Contributions:** Conceptualization, A.G. and K.K. ; data curation, J.S. ; formal analysis, A.G. and U.B.-M.; investigation, A.G.; methodology, A.G., K.K. and U.B.-M.; software, U.B.-M.; supervision, J.S. and K.J. ; visualization, A.G., J.S. and U.B.-M.; writing--original draft, A.G. and U.B.-M.; writing--review and editing, K.K. and K.J. All authors have read and agreed to the published version of the manuscript. **Funding:** This paper was written on the basis of the research projects funded by: Polish Ministry of Science and Higher Education--SUBB.WTD.19.036/2/2024. **Institutional Review Board Statement:** Not applicable. **Informed Consent Statement:** Not applicable. **Data Availability Statement:** This study was based on data from the following sources: 1. water quality reports on the Vistula River from the Municipal Water and Sewerage Company (MPWiK) in Warsaw, available at: [[https://www.mpwik.com.pl/view/badania-jakosci-wody-w-wwisle--wynik&i=745](https://www.mpwik.com.pl/view/badania-jakosci-wody-w-wwisle--wynik&i=745)]([https://www.mpwik.com.pl/view/badania-jakosci-wody-w-wwisle--wynik&i=745](https://www.mpwik.com.pl/view/badania-jakosci-wody-w-wwisle--wynik&i=745)) (accessed on 3 June 2024), 2. data obtained from the Chief Inspectorate for Environmental Protection (Poland) following a request for data, 3. data available as open data via the online data repository of the Chief Inspectorate for Environmental Protection (Poland): [[https://wody.gios.gov.pl/pjwp/publication/367](https://wody.gios.gov.pl/pjwp/publication/367)]([https://wody.gios.gov.pl/pjwp/publication/367](https://wody.gios.gov.pl/pjwp/publication/367)) (accessed on 3 June 2024).