Descriptive statistics of quantitative variables.

To strengthen cooperation among local governmental departments and improve water ecology, China has proposed the river management policy "river chief system + procurator". However, it remains to be verified that intergovernmental cooperative policies contribute to the improvement of China’s water ecology. Based on data from 87 national water quality monitoring sites released by the China Environmental Monitoring Station from 2015 to 2022, this paper constructed a multiperiod differences-in-differences model to evaluate the effectiveness of the cooperative governmental policy, the "river chief system + procurator", on the improvement of the water quality of rivers and lakes. The results of the study show that cooperative government policy helps to improve the water environment of rivers and lakes, which means that the implementation of the "river chief system + procurator" policy has significantly improved water quality conditions where implemented. In addition, further analysis revealed that intergovernmental cooperative policies had a limited impact on relevant indicators of river and lake pollutants that are more susceptible to different pollution sources compared to the comprehensive indicator of water quality class. This study helps further the understanding of the effects of cooperative intergovernmental policies and the policy practice of environmental governance in China.