Free-flowing river ecosystems are essential to the protection of biodiversity and the provision of ecosystem goods and services (1, 2). Yet, at a global scale, the flow and connectivity of most large rivers have been disrupted by the construction of dams to meet the growing population’s soaring demands for water, energy, and food production (3, 4). Consequently, freshwater biodiversity is now imperiled in most large river basins around the world, freshwater fisheries are collapsing, and estuarine deltas are shrinking due to sediment capture upstream (2, 5, 6). Much attention is now focused on mitigating the impacts of immense development in heavily modified river basins, but protecting the few remaining large free-flowing rivers is equally important, especially those where development is imminent (4, 7), such as the Salween River in southeast Asia.