Xia Yuanji (1366-1430) was appointed by the Yongle Emperor to take charge of water management in the Lower Yangzi Delta from 1403 to 1405. As is well known, the Yongle emperor ascended the throne by usurpation in 1402, and this article explores the relationship between Xia ' s water management and efforts to establish the legitimacy of the Yongle administration. It is contended here that Xia ' s appointment, his discourse on the sage-kings, and his choice of hydraulic strategies — as well as Yongle ' s attitude toward water management — were closely related and directed at bolstering Yongle ' s legitimacy. Taking inspiration from the theory of political ecology, I analyze the “ Three Rivers ” discourse formulated by Xia Yuanji from a political perspective. I argue that this discourse served to undergird Xia ' s approach to water management because it implied that Yongle was a sage-king in the mold of the Great Yu, who was of course highly admired for his benevolence toward the people. The “ Three Rivers ” discourse also provided a clear description of the waterway system in the Lower Yangzi and laid out an effective way of taking advantage of the work done by Xia ' s predecessors in the Yuan dynasty. Through an analysis of Xia ' s approach to water management, this article also intends to offer a reflection on current research methodology. While existing literature on water management mostly focuses on environmental changes and concrete hydraulic policy, this article proposes that it is also important to pay due attention to historical actors ' political expectations and to the cultural implications of certain discourses in order to obtain a better understanding of the significance and consequences of a particular policy. Viewing hydraulic issues from this angle, this article maintains that water management is often more appropriately understood as an action directed at a political purpose, and not simply a response to a natural catastrophe.