["Pacific Economic Review, EarlyView. ", "\nABSTRACT\nUsing data from national water quality monitoring stations, this paper constructs a city‐border‐year panel dataset of the transboundary river pollution in China. A difference‐in‐difference‐in‐differences (DDD) approach is employed to evaluate the effect of the River Chief System (RCS) on transboundary river pollution control. The results show that the RCS has heterogeneous effects on different pollution indicators, specifically alleviating COD and NpH levels, while deteriorating DO and NH3–N levels. The RCS has been, particularly, effective in improving transboundary river pollution control in large and medium cities. This improvement is mainly driven by reductions in agricultural fertiliser use and the upgrading of industrial structures. Finally, the study provides policy implications for implementing relevant water pollution control measures, such as the RCS, with a focus on effectively managing transboundary river pollution.\n"]