Despite policies aimed at sustainable sand mining, rampant illegal extraction continues in South Asia driven by profit motives, political patronage, and weak enforcement capacity. A study of sand mining in the Mahakali river in Nepal and the Teesta river in India reveals how gaps in implementation are exploited, with dramatic consequences for the local ecosystems. Addressing this complex challenge will require tackling the entrenched “sand mafia” nexus, building regulatory capacity at the local level, and promoting alternatives to river-based sand extraction.