Much has been learned from the basin of the Candelaria River, Campeche, Mexico: the fabric of a densely settled pre-Historic landscape, including impressive ceremonial centers; the logistics of an ancient entrepôt; the process of exploitation of dyewood and chicle in historic times; as well as the doubtful results of the mid-twentieth-century colonization of an “empty” forested basin. It also yielded the first evidence of more or less intensive pre-Hispanic wetland agriculture in the Maya region and the remains of a profuse network of fluvial transportation from prehistoric times to the present. This article presents recent evidence regarding the management of the river system itself by means of barriers, or “dams,” which facilitated agriculture in the wetlands upstream and extensive canoe travel. These structures seem to be elaborations or imitations of the numerous natural barriers already in the stream. Two models help explain context and function. It has become apparent that the human interventions into the wetlands and the river system are to be seen less as great attainments of civilization than as fairly desperate expedients in the face of climate change.