Tonle Sap is the massive freshwater lake that dominates the map of Cambodia. The lake is at once a reservoir, flood-relief system, communications route, home and larder to the people who live on and around it; even Cambodians who live nowhere near depend on it as a rich food source. The lake is home to rare and endangered water birds and is unique for its flow of water, which changes direction twice a year. With the change in seasons, the lake has the ability to expand and shrink dramatically. At the height of the wet season, the lake can be more than 7,400 square miles (12,000 square kilometers) and provides half of the fish supply for Cambodia.

The lake was designated a UNESCO Biosphere Reserve in 1997 – a status which reconciles sustainable use with conservation. One core area of the reserve, Prek Toal, is a sanctuary for a wide range of water birds, including three endangered species – spot-billed pelicans, greater adjutant storks, and white-winged ducks.

Trips are most interesting time during the dry season, when you'll see people fishing in the backwaters and children punting themselves to school as your boat heads down narrow creeks and along the river to reach the lake itself.