Abstract: As critical actors in water environment governance, the multi-stakeholder participation of governments, enterprises, and the public exerts significant influence on governance efficiency.In this study, we analyze panel data from 11 provinces and municipalities in the Yangtze River Economic Belt (YREB) from 2012 to 2021.Methodologically, we measure water environment governance efficiency(WEGE) using a super-efficiency SBM-DEA model, construct a distance-weight matrix based on total water resources, and employ spatial econometric techniques (spatial Durbin model, SDM) combined with a panel threshold model to quantify the impact of multi-stakeholder participation on WEGE.Furthermore, a mediation model is employed to examine the roles of government green innovation incentives and corporate green transition.Key findings include: ① Multi-stakeholder participation significantly enhances WEGE.② Collaborative interactions among stakeholders improve regional governance outcomes, although the effectiveness varies significantly across the upper, middle, and lower reaches of the Yangtze River.③ Government green innovation incentives and corporate green transition effectively improve WEGE through mediation effects.④ Threshold effects emerge when stakeholder engagement reaches critical levels.This research provides theoretical foundations and policy recommendations for optimizing multi-agent governance mechanisms in the Yangtze River Economic Belt, advancing sustainable development of regional water environments.