This paper aims to examine the Tseng-Wen Reservoir Trans-basin Water Diversion Project from the perspective of environmental justice, and to explore the disputes on the distribution of interests and environmental risks of the project, and the policy implications of local action. It reveals the multiple perspectives of stakeholders on the project, the various knowledge claims among experts of different disciplines, and conflicts between local knowledge and the experts. The authorities have framed the project as either a water supply effectiveness issue or an economic development issue.