In order to improve the water quality of the downstream stretch of the Xin’an River, in 2011 China implemented the Ecological Compensation Initiative, a pioneering policy establishing side payments between upstream and downstream provinces. This column shows that the initiative mitigates cross-border externalities by sharply reducing water pollutant emissions by upstream firms and also induces firms to relocate to neighbouring cities. The findings highlight the potential for bilateral compensation for ecosystem services to reduce pollution.