Tonle Sap Lake is one of the largest freshwater lakes in Asia, and one of the most unique ecological water wonders in the world. It was designated as a protected area under UNESCO’s Man and Biosphere programme in 1997.

The lake is swelling to an expansive 12,000 square meters. During the dry half of the year the Lake shrinks to as small as 2500 square meters, draining into the Tonle Sap River.

But during the wet season a unique hydrologic phenomenon causes the river to reverse direction, filling the lake instead of draining it.

The engine of this phenomenon is the Mekong River, which becomes bloated with snow melt and runoff from the monsoon rains in the wet season.

The swollen Mekong backs up into the Tonle Sap River at the point where the rivers meet at the ‘chaktomuk’ confluence, forcing the waters of the Tonle Sap River back upriver into the lake. The lake is located just about 15 km south of Siem Reap town.

Visitors can take the ferry between Phnom Penh and Siem Reap by crossing the lake and dock at the village of Chong Khneas.