The Sirvan River is a vital freshwater source in Kurdistan Province, flowing through both urban and rural landscapes. Its proximity to human settlements, agricultural zones, and livestock operations increases the risk of contamination from untreated wastewater and surface runoff. Consequently, microbial monitoring of surface water within this watershed is essential for evaluating the region’s sanitary and environmental conditions. Microorganisms in aquatic ecosystems, beyond their ecological functions, are widely recognized as reliable indicators of water quality. Fluctuations in microbial populations often signal the presence of pollutants such as domestic sewage, animal waste, and nutrient compounds (Bradshaw et al., 2016). Among these indicators, coliform bacteria particularly fecal coliforms and Escherichia coli are of critical importance due to their intestinal origin and thermotolerance, making them precise markers of contamination from human and animal sources (Aenab and Singh, 2015). Numerous international studies have explored the factors influencing the presence and distribution of indicator bacteria in surface waters. For example, Pall et al. (2013) and Islam et al. (2017) examined the roles of temperature, precipitation, land use, and wastewater treatment efficiency in microbial load variation. Newton and McMahon (2011) investigated the relationship between organic and inorganic compounds and microbial community structure in lakes. At the watershed scale, Flood et al. (2022) highlighted the influence of geological and hydrological features on microbial contamination in rivers. Similarly, Park et al. (2021) demonstrated the impact of vegetation cover and land slope on bacterial distribution in South Korea. In Iran, several studies have addressed microbial water quality. Roshani-Sefidkouhi et al. (2025) assessed the Chahnimeh reservoirs in Sistan and Baluchestan Province, while Khatib Haghighi and Ghaani (2018) evaluated urban and rural drinking water sources in Gilan Province using total and fecal coliform indicators. However, most of these investigations were limited to cross-sectional designs or specific seasons. Comprehensive studies on spatial and seasonal variations of microbial indicators in Iranian rivers particularly the Sirvan River remain scarce. This study presents a year-long monitoring of microbial indicators, including total coliforms, fecal coliforms, and E. coli, across six stations in the Sirvan River watershed, covering a full hydrological cycle (July 2023 to June 2024). By analyzing seasonal and spatial trends and examining the influence of surrounding human activities, this research offers a novel approach to surface water quality assessment. The findings aim to identify pollution hotspots, evaluate sanitary conditions, and inform water quality management strategies for Kurdistan Province and similar regions.

Discussion and conclusion 

The elevated bacterial concentrations observed in downstream stations (2, 3, and 4) of the Sirvan River reflect the impact of human activities, including the discharge of untreated or partially treated sewage and agricultural runoff (Helmer and Hespanhol, 1997; Agarwal and Rajwar, 2010; Aenab and Singh, 2015). These conditions are exacerbated by warm water temperatures, reduced flow rates, increased evaporation, and higher pollutant loads factors consistent with microbial contamination patterns in similar ecosystems (Rusiñol et al., 2020; Rather et al., 2023; Al-Afify et al., 2023). The presence of E. coli in elevated concentrations is a clear indicator of fecal contamination and poses serious health risks to communities near the river. The findings highlight the inadequacy of existing wastewater treatment systems and the urgent need for infrastructure upgrades to mitigate pollution. Lower bacterial concentrations at upstream sites suggest the effectiveness of natural filtration by vegetation, topographical separation from pollution sources, and hydrological buffering (Yaghoubzadeh and Safari, 2016; Wang et al., 2022). This study reinforces the importance of regular microbial water quality monitoring in the Sirvan River watershed using robust indicators such as E. coli. Effective management requires prioritizing the identification and control of both point and non-point source pollution, especially during peak contamination seasons. Strategies should include improved wastewater treatment, public awareness campaigns, and ecological restoration of water bodies. Integrated watershed management, supported by collaboration among water, health, and environmental authorities, is essential for safeguarding water quality and public health.

Conflict of interest