Songkran Festival
The Songkran Festival Chiang Mai heralds in the Thai New Year with a mass of religious ceremonies held over 3 days to mark the beginning of the solar year.
For foreigners, Songkran is best known for being the biggest water fight in the world, when locals and foreigners alike splash water at each other all over the city.
source: https://www.chiangmaitravelhub.com/events/songkran/