ABSTRACT Environmental phenomena shed light on the fiction that inter-state borders constitute on some level, and the limitations of state-based environmental governance. Transboundary watersheds, in particular, flow across borders of different kinds, evincing the interdependence of water bodies, both human and nonhuman. The lack of cross-border comprehensive environmental governance imposes regional forms of inequity and inefficient forms of water protection. In Central America, to address such problems, citizens have created a legal prototype for how transboundary watersheds could be governed as a commons going forward. This endeavour has been led by Salvadorans, concerned as they are by their country’s position as a lower co-riparian and their significant interdependence with transboundary water bodies. I argue that, in addition to destabilizing established approaches to environmental governance, the legal prototype opens avenues for forms of earthly politics and multispecies justice by placing the reproduction of life, human and nonhuman, side by side.