There are approximately 170 floating villages that line the perimeter of lake Tonle Sap, the largest fresh water lake in southeast Asia. Over 2.7 million people live in these villages. Each year, after the rain season, the Mekong River backs up into lake Tonle Sap and increases its area significantly. The houses, schools, stores, etc., of the floating villages move to accommodate this change in the lake's geography. When the dry season comes, the lake starts draining back out to the Mekong River again, and the villagers must again relocate their structure.