"For a monk to walk freely with crowds of ordinary people during the water festival violates the rules of the Lord Buddha," the patriarch said.
"If the monks walk freely, they will see women wearing sexy clothes or see people kissing. This violates their discipline," he said. He added some younger monks carried mobile phones equipped with cameras at last year's festival and took pictures of people dancing, drinking alcohol and kissing — all of which are not allowed, including the possession of cellphones.
Monks are supposed to adhere to a code of Buddhist precepts that include celibacy and not touching or being alone with women, not drinking alcohol and leading a contemplative lifestyle without material possessions.
A committee has been created to curb bad behaviour among monks and if any are seen mingling at the festival they will be reprimanded and sent for a re-education class before being returned to their temples, Non Gneth said.
Authorities estimate upward of 2 million people could descend on the capital, Phnom Penh, for the annual boat festival, also known as the water festival, which takes place at the end of the rainy season along the Tonle Sap River.
Some 400 wooden boats will compete in rowing contests that are part of a carnival-like atmosphere that also includes evening concerts, fireworks and late-night partying.
About 85 per cent of Cambodia's 14 million people are Buddhist. The country has 4,000 Buddhist temples and more than 50,000 monks.