The boat races are the heart of the festival. Teams of up to 80 rowers sit in long, low, brightly decorated wooden boats called 'ngo' - carved and painted to look like dragons, nagas (serpents) or other mythical creatures. They race in pairs along the river, with the riverside packed with cheering spectators.
The festival also celebrates the Tonle Sap's unique reversal. When the Mekong floods each year, it pushes backwards up the Tonle Sap river until the current flows the opposite direction for several months. When the monsoon ends, the water retreats and the river flows normally again. Cambodians celebrate this natural event as a kind of gift - the flood brings fish and fertile mud to the land.
At night, small illuminated boats called 'floating lanterns' are set on the water, drifting downstream with lit candles inside. The river at night during the festival, with hundreds of lanterns and bright lights from the city reflected in the water, is described by visitors as one of the most beautiful sights in Southeast Asia.
Villages from across Cambodia send their best boat teams to compete. Training begins months in advance. Being chosen to row in the Water Festival boat is a great honour, and teams practice on rivers early in the morning throughout the racing season.