The complexity of water-related challenges requires multilevel management and coordination in the governance system. Despite many efforts to promote Integrated Water Resources Management (IWRM) in national and international policy arenas and even adopted in national water laws and regulations, IWRM implementation in practice has faced many problems. Lack of inter-sectoral (regional) coordination and weak capacity of river basin organizations are among the most critical obstacles of IWRM implementation. This study aims to understand the coordination mechanisms in the Zayandeh Rud basin's water governance structure and process. We used the Management and Transition Framework (MTF). The research objectives are to describe and understand the stated problem, and the research questions are what and why types. The research strategy is an in-depth case study, and quantitative and qualitative methods are applied in data collection and analysis. The data were collected through document analysis and process tracing approach and in-depth interviews with experts, administrative, and stakeholders of water and agricultural sectors in the Zayandeh Rud basin. The results showed that despite the formal provision of coordination mechanisms in Iran's laws and regulations, these mechanisms are not very diverse and more focused on physical meetings. In practice, coordination ineffectiveness is evident. Although hybrid governance mode-including hierarchy and network styles-prescribes in the de-jure vertical and horizontal coordination, the top-down command of the state is dominant in de-facto practice, due to the centralized structure, lack of synergy between different governance modes, trade-off among the goals of formal and informal institutions. Also, the policy incoherence plays a significant role in the ineffectiveness of coordination mechanisms. There is a high level of incoherence in policies, especially in Iran's five-year development programs. The dominance of the centralized, top-down, and fragmented planning in the five-year development programs has led to simple blueprint panaceas for the country's whole. Also, lack of traarency in information on the water consumption of different users and water availability in the basin, missing low-cost and fast compliance assurance system for monitoring and enforcement of laws and regulation and the accountability gap in return of actors powers and decisions were identified as other obstacles of proper coordination. Considering the importance of stakeholder participation in water resources management, shifting from the dominant hierarchical mechanism in basin coordination processes to more diversified coordination styles and designing problem-solving forums to engage stakeholders in fact-finding, data gathering, knowledge-sharing, participatory monitoring, and the adoption of a consensual strategy, are of paramount importance. Key Words : De-jure and de facto coordination, Diagnostic approach, Governance functions, Management and Transition Framework, Zayandeh Rud River.