Rivers have long been convenient yet troublesome borders. Inherently itinerant, rivers routinely defy cartographic depictions of borders as static, territorially bounded formations. Such dynamism poses material and conceptual challenges to state regulatory activities, resulting in increasingly heterodox attempts to fix waterbodies through various securitizing mechanisms. I examine the dialectical relationship between rivers and borders through the concept of the river-border complex. I ask how the Ganges River shapes the form and function of the Indo-Bangladeshi border and how, in turn, bordering practices in India regulate flows along the river, which comprises 129 km of India's border with Bangladesh. Drawing on archival records, in-person interviews, and river data, I find that the border and efforts to secure it mediate many flows along the river. The study corroborates previous work within critical border studies that securitizing cross-border flows has the perverse effect of generating greater insecurity in adjoining countries. Crucially, historical analysis of sediment, information, and human flows reveals how international rivers also determine patterns and processes of circulation and thereby warrant reconceptualization as border infrastructures, rather than as merely being subject to them. [ABSTRACT FROM AUTHOR]