For three days, workers from every province join with the city's residents to celebrate by night and day. The festival lasts three days, and commemorates the end of the country's rainy season, as well as the change in flow of the Tonle Sap River. It includes boat races and concerts, and attracts several million people each year.
Phnom Penh resumed Water Festival celebrations in 1990, following a 20-year break under the Lon Nol regime and then the genocidal Khmer Rouge. A few of Phnom Penh's many foreign residents started participating in the featured boat races in the mid-1990s, though in the first year of participation their boat capsized, along with two other teams, in the wake of a larger ship. In 2008, five rowers drowned and a single rower drowned in 2009 during the boat races.
The celebration turned tragic in 2010, when thousands became trapped and stampeded off the bridge between Phnom Penh and Diamond Island, killing 351 people and injuring 395 more. Rumors spread that it was caused by fear of a coming storm or electrical shock from faulty wiring, and authorities ultimately laid blame on the swaying of the bridge.
Phnom Penh authorities came under fire in 2016 for sanitation, after videos of cleaning crews sweeping trash into the Tonle Sap incited anger on social media.
According to wikipedia