A thorough study “is essential for evaluating the long-term consequences of interlinking rivers,” says V. Rajamani, a geologist at Jawaharlal Nehru University in New Delhi. Flooding, he notes, is a natural process that enriches basins with silt deposits. Key issues, such as the effects of sedimentation loss and alterations in water and nutrient supply, “are huge unknowns,” he says. Those uncertainties could make the Interlinking of Rivers Project a $120 billion gamble.