Impact of anthropogenic pollution on lake ecosystem: a review of Koka and Ziway lakes in the Central Rift Valley, Ethiopia

Abstract

Lakes Koka and Ziway in the Central Rift Valley (CRV) of Ethiopia are essential socio-ecological systems that provide water for domestic use, irrigation, hydropower, and fisheries, while also sustaining diverse biological communities. However, these lakes are under severe ecological stress due to intensifying anthropogenic pollution from industrial, agricultural, and urban sources. This review synthesizes multidisciplinary evidence on pollution sources, types, and ecological consequences, focusing on impacts to water quality and ecosystem services. Physicochemical data reveal that concentrations of heavy metals, nutrients, and organic pollutants regularly exceed World Health Organization (WHO) guidelines, with alarming levels of nitrate, phosphate, lead, chromium, and cadmium observed in both lakes. Agricultural runoff, industrial effluents, and untreated municipal wastewater emerge as primary pollution sources. These contaminants drive eutrophication, biodiversity loss, and the decline of fisheries, thereby undermining livelihoods and exacerbating water insecurity. Invasive species such as water hyacinth further degrade aquatic habitats, while sedimentation alters hydrological dynamics. The review highlights the flowing impacts of pollution on ecosystem services, including disruption of water supply, economic loss, and health risks. It also identifies knowledge gaps and emphasizes the need for integrated watershed governance, investment in wastewater treatment technologies, adoption of sustainable agricultural practices, and enhanced community participation. The review underscores the urgency of adopting a multisectoral response grounded in Integrated Water Resources Management (IWRM), emphasizing collaborative governance, technological innovation, and community-led stewardship as pathways to restore and sustain the health and services of lake ecosystems in the CRV.