Evolution and Mechanism of Intergovernmental Cooperation in Transboundary Water Governance: The Taihu Basin, China

Transboundary water governance faces persistent challenges due to mismatches between natural hydrological boundaries and political administrative boundaries. This study examines the evolution and mechanisms of intergovernmental cooperation in the Taihu Basin (1987–2024), addressing how cooperation forms, evolves, and sustains amid conflicting priorities. Using a mixed-methods approach, we analyzed 106 policy documents, government reports, and stakeholder interviews to map governance stages, cooperation networks, and policy themes. Results reveal three phases in transboundary water governance in Taihu Basin: (1) a centralized hierarchy (1987–2007) dominated by vertical mandates; (2) a hybrid stage (2008–2018) with rising horizontal cooperation driven by crisis responses like the 2007 cyanobacteria outbreak; and (3) a networked stage (2019–2024) integrating diagonal mechanisms that bridged hierarchical gaps and scaled grassroots innovations. Key findings show diagonal relations reduced bureaucratic delays, enabling bottom-up practices like joint river chief systems to become regional policies. While grounded in the Taihu Basin context, this study provides a compelling case of institutional coupling that may inform governance in other transboundary basins, where vertical authority, horizontal reciprocity, and diagonal experimentation coexist dynamically. This study offers a model for balancing administrative fragmentation and ecological integrity, emphasizing adaptive networks over rigid hierarchies. These insights provide a feasible solution approach for addressing transboundary water resource governance challenges in similar institutional environments.