What is the reason for the 'Cambodian Water Festival', a three day festival celebrated on the full moon in November?

Bon Om Touk, also known as the Cambodian Water Festival, is a three day festival celebrated on the full moon in November.

The festival marks a reversal of the flow between the Mekong and Tonle Sap rivers. Due to the amount of water deposited during the rainy season, the Tonle Sap river becomes so swollen with water that it reverses the direction of its flow and flows upstream to Tonle Sap lake.

The festival marks the switching of the flow back to its normal direction, signifying the end of the rainy season. Essentially, the festival is a time to give thanks to the rivers as they provide the region with fertile farming land and plenty of fish.

The festival is focused on boat races and concerts. The roots of the boat races can be traced back to the times of the Angkorian kings who would train and evaluate the fighting skills of their water based warriors by holding competitions on the river. These trials in turn honoured the naval victories of the Khmer empire under the leadership of Jayavarman VII in the twelfth century.