<p>River ecosystems provide a wide range of services that enhance the quality of life of stakeholders, yet they remain among the most vulnerable zones of human nature interaction. Evaluating ecosystem services and identifying affected stakeholders is essential for sustainable river basin management. This study evaluated the ecosystem services and stakeholder groups of the Tajan River Basin in Mazandaran Province of northern Iran. Research data were collected in 2024 through Delphi questionnaires completed by 19 experts in river and water sciences. The Delphi technique and Multi-Criteria Decision-Making (MCDM) methods such as TOPSIS, ARAS, and SAW were used to identify and prioritize ecosystem services, sub-services, and stakeholders. Due to differences in the prioritization results of the MCDM methods, the Copeland integration method was applied for final prioritization. The evaluation identified 15 ecosystem services, 27 sub-services, and 12 stakeholder groups. The results showed that water supply, hydrological cycle and water flow regulation, recreation and ecotourism, natural hazard regulation, and food supply services ranked highest among the ecosystem services. In the sub-services section, drinking water supply, water storage to reduce drought risk, agricultural water supply, surface water flow regulation, and groundwater recharge were prioritized. Regarding stakeholders, farmers were ranked as the top priority group. The results also indicated that regional government organizations, related national organizations, households and residents, and future generations are important stakeholders in the Tajan River Basin. Comprehensive evaluation of river ecosystem services and stakeholders enables regional prioritization, streamlines planning, reduces costs and complexity, and supports effective, inclusive river basin management and conservation.</p>