Every year the Mekong River backs up and increases the size of Tonle Sap, the largest lake in Southeast Asia, from 2700 to 16000 square km.  A prime breeding ground for fish, Tonle Sap is responsible for 75% of Cambodia's inland fish catch, and 60% of it's protein intake.  Unfortunately, pollution (you can see in green), and planned dams along the Mekong threaten the lake, and the people who depend on it.