Cambodia’s Lake Tonle Sap is a fish factory, powered by an annual pulse of water—flooding and receding in the lower Mekong River basin to which it’s connected by the Tonle Sap River. About 80 percent of the protein Cambodians eat is fish, which makes the Tonle Sap indispensable for a growing nation’s food security. But Cambodia and its neighbors also need other things from the water that flows through the lower Mekong Basin—for irrigating rice and other crops, for expanding hydropower and supporting booming cities. All these needs are real, but coupled with a changing climate, they could put the Tonle Sap at risk. Can a new approach to conservation on the lake keep it all in balance?