Seasonal assessment of water quality in an urban stretch of the Neves River, Northeast Brazil

Introduction: Rivers constitute one of the main sources of freshwater for living beings. However, they suffer constant environmental impacts that may compromise their quality. Objective: Therefore, this study aimed to evaluate the seasonal bacteriological quality of the Neves River in São Raimundo das Mangabeiras, Maranhão, Brazil. Methodology: Water samples were collected monthly at four points for six months, between 2023 and 2024, including the dry and rainy seasons. In the field, the temperature and pH of the water were measured, and an ecological evaluation protocol was used at each point. Water samples were used to quantify mesophilic bacteria, total and thermotolerant coliforms, and to assess the presence of Escherichia coli (E. coli), Salmonella, and coagulase-positive Staphylococcus under laboratory conditions. Results: It was demonstrated that 50% of the evaluated points had a high degree of environmental impact. Water temperature ranged from 27.5°C to 29.8°C, and pH from 6.1 to 7.0, without major oscillations between the seasons. However, during the rainy season, the highest number of mesophilic bacteria, coliforms (total and thermotolerant), and the greatest presence of E. coli (58% of the evaluated samples) were detected. The presence of Salmonella or coagulase-positive Staphylococcus was not detected. Conclusion: Therefore, it was verified that some urban stretches of the Neves River have low water quality, mainly during the rainy season. Thus, it was recommending the urgent adoption of public policies to minimize the environmental impact on this river.