Introduction: Surface water may contain toxic substances and pathogenic microorganisms, which can adversely affect the environment and human health. Various fertilisers and pesticides are often used in agriculture. These can pass into standing bodies of water, into the sea, or they may remain in the ground, thus endangering plants and animals in watercourses. Purpose: The purpose of this study was to assess the chemical and microbiological state of the Ščavnica river before and after the outflow of municipal wastewater from the Ljutomer and Razkrižje water treatment plants, and to determine their impact on the watercourse. Methodology: We monitored the microbiological and chemical parameters of the Ščavnica river at six sampling sites for one year. The samples were analysed based on chemical and microbiological parameters. We used the spectrophotometric method with cuvette tests and a BOD5 measurement system for the chemical analyses. In order to detect E. coli and enterococci, we used the method of membrane filtration. Results: The values of the parameters measured fluctuate from season to season. The number of microorganisms is higher in summer than in winter, however, this does not hold true for chemical parameters, as their values vary considerably from month to month. The highest values of chemical parameters were found at sampling points 4 and 6, which are located after both of the treatment plants. The Razkrižje treatment plant’s impact on the Ščavnica is smaller than that of the Ljutomer treatment plant, but the former also connects to fewer inhabitants. We also confirmed increased values in most of the monitored parameters in sample 1, which was taken just after the Gajševci accumulation lake. In sample 3, which was located right after the sewage discharger in Ljutomer, we detected an increase in the number of microbiological parameters and ammonia. Discussion and conclusion: Based on our results, we found that the Ljutomer and Razkrižje treatment plants affect the quality of the water in the Ščavnica river since the river's quality after the outflow of municipal wastewater is worse compared to the sections before the outflow from the treatment plant. However, these values are not high enough to conclude that this is a river of low quality. Here, we should also mention diffuse sources of pollution, especially agriculture with nitrogen emissions, which also decrease the quality of the Ščavnica river.
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