Assessing river health in North Gondar, Ethiopia: an integrated assessment of physico-chemical parameters and benthic macroinvertebrate communities

The pollution of freshwater systems by human activities is a significant global issue, intensified by population growth, industrialisation and urban development. Physico-chemical parameters and benthic macroinvertebrates were assessed in the Asera and Zarima rivers, Gondar Zone, Ethiopia, using data collected from October 2024– January 2025 and February–April 2025. Nineteen benthic macroinvertebrate species were recorded, representing 13 orders and 19 families. Diversity indices, including the Shannon–Wiener index, indicated that both rivers were mainly disturbed, with spatial and seasonal variations in ecological conditions. The Asera River served as a critical dry-season sanctuary, although macroinvertebrate diversity was lower at the upper site. The upper reach of the Zarima River showed maximum macroinvertebrate diversity during the wet season. Anthropogenic pressure was identified as the major factor influencing community composition, demonstrated by the dominance of pollution- tolerant taxa, particularly Chironomidae. Physico-chemical analyses supported these observations, with elevated biological oxygen demand, chemical oxygen demand, and phosphate levels indicating severe organic pollution. Overall, both rivers showed ecological degradation, emphasising the urgent need for effective conservation and management measures.