The Water Festival, a spectacle to behold, is probably the most exorbitant festival held each year in November. It is usually celebrated for three days, i.e. the 14th and 15th of the waxing moon and the 1st of the waning moon of the month of Kadek. The 15th of the waxing moon is the last full moon day.

The festival ushers in the fishing season, marks a change in the flow of the Tonlé Sap and the ebbing-water season, and is seen as thanksgiving to the Mekong River for providing the country with fertile land and abundant fish.

At the height of the rainy season, the water of the Mékong River forces the Tonlé Sap to reverse its current and to flow up to the Tonlé Sap Lake. As the water of the Mékong River begins to subside, the swollen Tonlé Sap Lake flows back to the Mékong River through the Tonlé Sap and empties into the sea, which leaves behind vast quantities of fish. This, indeed, is a remarkable phenomenon of the Tonlé Sap.