The days when the gigantic Indian rivers — the Ganges, Indus and Brahmaputra — roar freely down the steep slopes of the Himalayas may be numbered. Roughly 300 dams are proposed or under construction in the deeply cut valleys of India’s mountainous north, part of a massive effort to meet the country’s spiralling energy demands. But the projects are facing fierce resistance from local communities, as well as from scientists who predict that the dams’ ecological impacts will be much greater than official environmental assessments suggest