<p>This article examines the emergence of river basin development within Colombian regional governance. It traces the creation of the Corporación Autónoma Regional del Valle del Cauca—a regional authority modeled after the Tennessee Valley Authority—from the formulation of its basin program in 1954 to the approval of the Calima Dam in 1960. Drawing on board minutes, reports, and expert accounts, it shows how distinct epistemic practices and ways of knowing were brought into relation through the production of the basin as a spatial scale, a jurisdiction, and a framework for territorial planning and development. Yet the basin form was also a site of contestation, as landowners, peasant communities, state officials, and financial institutions challenged the program’s common notions of economic development, governance scale, and regional authority. In doing so, the article contributes to scholarship on the co-production of hydrological knowledge, economic expertise, and the modern state in Latin America by providing a critical historical account of a river basin governance program conceived and implemented during the early years of Cold War development.</p>