Naga Fireballs (Bang Fai Phaya Nak) on the Mekong

The fireballs are said to be reddish, from the size of a spark to the size of a basketball, rising quickly and silently from the water to a couple of hundred meters before they fade. They've been reported along about 250 km of the Mekong centered on Phon Phisai, and occasionally from smaller rivers and ponds nearby. Until the mid-1980s locals called them ghost lights, before the council renamed them phaya nak lights.

The legend ties them to the end of Lent. The Phaya Nak, the great serpent believed to live in the Mekong, is said to breathe the fireballs into the sky to welcome the Buddha back to earth after he spent the Lenten season preaching to his mother in heaven. That's why the night matters as much as the lights. It's a religious occasion first, with merit-making at the temples, and the fireballs are the climax.

Nobody has proved what causes them. The best-known natural explanation is that marsh gas, usually named as phosphine or methane, bubbles up from the riverbed and ignites, and others have pointed to plasma effects. The skeptic writer Brian Dunning argues that burning gas bubbles couldn't ignite on their own or stay lit at the speed the fireballs rise.

The human explanation is louder. A 2002 iTV documentary filmed Lao soldiers firing tracer rounds into the air across the river during the festival, and Jessada Denduangboripant, a science professor at Chulalongkorn University, says the fireballs are tracer bullets fired by villagers on the Lao bank. He points to slow-shutter photos that show red streaks rising from the ground, and to the fact that the fireballs come on the night after the full moon, when Lent ends, rather than on the full moon itself.

Interest has dipped as the debate has grown. Nong Khai counted about 31,500 visitors in Rattanawapi and Phon Phisai on the night in 2025, down from 141,381 in 2024, and 287 fireballs, down from 371. You don't have to settle it to enjoy the night. Sit by the river, watch, and make up your own mind.

Ok Phansa is one of the great festival times on the Mekong, and Nong Khai runs a program over several days. Expect long-boat races on the river, illuminated fire boats drifting downstream after dark, processions, Naga worship ceremonies, Tak Bat Thewo merit-making when monks collect alms, walking streets and food markets wherever there's room for a grill.

Make a day of it. Spend the afternoon in Phon Phisai or Rattanawapi, eat at the stalls, watch the ceremonies at sunset and settle in by the river before dark. Bring water, something to sit on, mosquito repellent, a charged phone, cash and patience, and fill the car with fuel before you reach the busiest area.

Phon Phisai and Rattanawapi have very few rooms, and they go first. Most visitors stay in Nong Khai town, on the Mekong, with guesthouses like the long-running Mut Mee Garden and riverside hotels, and drive or take a tour to the viewing areas. Udon Thani, a bigger city with the airport, is the other base, with more hotels and a longer drive on the night. Either way, book as soon as you know the date.

For many of the people around you this is a religious night, whatever you believe about the lights. Dress modestly at the temples, keep your voice down during the ceremonies, and don't scoff at the Naga in front of people praying to it. Take your rubbish with you, and leave the riverbank as you found it.