The annual three-day Water Festival competes with the Khmer New Year for being the most important holiday for Cambodians.
The boat races on the Tonle Sap and the carnival atmosphere ashore attract millons of people from all over the country.
A smaller Water Festival is held around Angkor Wat, but for the real thing you'll have to go to Phnom Penh.
In Khmer the annual Water Festival is called Bonn Om Toeuk. The Water and Moon Festival ushers in the fishing season.
It also marks the reversal of the current in Tonle Sap river. Boat races as well as fireworks displays are held at the river.
After the tragic events on the last day of the festival in 2010, it was canceled the following year. Festivities were also scrapped in 2012, after the death of the King's Father, Norodom Sihanouk.
Date in 2013: November 16-17-18
More than 400 boats, propelled by precision-trained oarsmen, take part in the annual boat race, the highlight of the Water Festival or Bonn Om Touk. This is one of the major events in the Kingdom which attracts multitudes of people from the various provinces to the capital Phnom Penh.
They arrive by buses, cars, bikes, cyclos, bicycles and even trucks. Many stay over in the city during the three-day festival, lending support to their boat team. Others use this opportunity to explore the sights and sounds of Phnom Penh - for many it is the only occasion to visit the city.
Reversal of the river
The Water Festival also marks a unique natural phenomenon - the Tonle Sap river reverses the flow of its current. It is probably the only waterway in the world which flows in opposite directions at different times of the year.
The Tonle Sap lake or Great Lake is a vast expanse of water, once an arm of the sea, which forms the most significant topographical feature in country. The lake is fed by the Mekong river and the Tonle Sap river.
From November to May, the Tonle Sap river runs into the Mekong just like any other tributary.
But with the arrival of the monsoon rains, there is such build-up of water in the main stream that excess pours into the Tonle Sap river, forcing it to change direction and flow back into the Tonle Sap lake.
Full Moon brings good luck
The Festival also coincides with the full moon of the Buddhist calendar month of Kadeuk. The Cambodians believe that the full moon is a good omen which promises a bountiful harvest.
On this night, especially in the countryside, people gather to give thanks to the moon. Special food is prepared for this occasion - fruits, vegetables and fish amok, a uniquely Cambodian speciality. Candles are lit, incense burnt and offerings made. The chief priest lights the candles and as it drips on the banana leaves spread beneath the candles, predictions are made. It is said that the shape of the melted wax on the banana leaves dictates the state of all future harvest for the year.
Carnival in Phnom Penh
It is not surprising that the city takes on a carnival air during this period. Open-air live concerts are held, make-shift food stalls selling a variety of local fare are set up in parks and children as well as adults take rides on ferris wheels.
Colourful buntings and banners adorn government buildings and as night falls the Royal Palace is brightly lit with colourful lights. Brilliant fireworks illuminate the night sky and flotillas, outlined by lights, glide gracefully down the river. This is, in fact, Cambodia's version of the Mardis Gras.
See more pictures of Phnom Penh Water Festival