Tonle Sap Lake located South of Siem Reap City is the largest lake in Cambodia and plays an integral part in the ecological balance of the country.

In the dry season it is a shallow lake which drains through the Tonle Sap River into the Mekong River at Phnom Penh. However this changes in the June - November monsoon season when the high water level of the Mekong River causes a reverse flow up the Tonle Sap River into the lake area. The inflow increases the size of the lake from its low of 2500 square kilometres to over 10,000 square kilometres. This makes the lake the largest freshwater lake in the South East Asia during the wet season.

The flooded mangrove forest plains are home to over 100 varieties of water birds including a number of threatened or endangered species. There are over 200 varieties of fish in its waters as well as crocodiles in maroques otters and turtles.

The lake is populated with floating villages inhabited by both Cambodian and Vietnamese communities. The individual villages are an amazing sight with their floating houses, markets, schools and churches. The villagers earn a living from fishing with their huge fish traps catching enough to supply Cambodia with half of its fish consumption.

One of more prominent floating villages is Chong Khneas. It is 12 kilometres south of Siem Reap and is a departure/arrival point for the Phnom Penh ferry service and also Tone Sap lake tourist trips.

While this floating village is a well known landmark, the tuk tuk driver who brought the group from Siem Reap claimed that less tourist orientated villages of Kampong Pluk and Kampong Khleang gave more of an insight into lake life. Both these villages are south of Chong Khneas on the eastern side of the lake. Kampong Khleang is actually the largest floating community on Tonle Sap .This Vietnamese settlement also has a thriving pottery industry as there were stacks of clay pots in front of most of the houses.

To the west of Chong Khneas at the northern end of the lake is the Prek Toal Bird Sanctuary. This reserve is and has been called the most important breeding ground in South East Asia for large water birds. Species such as the Black-headed ibis, spot billed Pelican, Grey headed Fish Eagle, Painted Stock and Millet Stork nest in the area. The sanctuary is most popular with bird watchers in the dry season months when flocks of migratory birds visit the area.

During the dry season the lake water flow reverses with the inflow into the Mekong River providing a necessary balance to the river south of Tonle Sap. The fresh water flow into the Mekong Delta of Vietnam provides a buffer to the salt headwaters of the South China Sea entering the delta's agricultural lands.