Nearly 20 million people live in Southeast Asia's Mekong Delta, which is also the source of 7–10% of internationally traded rice. But the delta will be nearly entirely underwater by the end of the century if water management practices in the region don't change. Avoiding this scenario will require significant, coordinated action from all six countries in the Mekong basin, argues a multidisciplinary, international research team in a commentary published today in the journal Science.