The Tonle Sap lake does something remarkable every year. In the wet season (around June to October), the Mekong River fills up with so much water that it actually pushes backwards into the Tonle Sap, making the lake grow to five times its dry-season size. Then in the dry season, the water flows back out and the lake shrinks again.
The floating villages move with the water. When the lake rises, the whole village drifts outward. When it falls, the village drifts back in closer to the shore. Everything floats - the school building, the temple, the market stalls and the petrol station.
Children in the floating villages travel to school by small boat. In the dry season, the lake is so shallow in places that you can wade across parts of it. In the wet season, the same places might be three or four metres deep. The children know the lake in a way that land children never could.
The lake is extraordinarily rich in fish. Around a million people near Tonle Sap work in fishing. The fish they catch - and preserve, and dry, and ferment - are eaten all over Cambodia and are the source of much of the country's food.