Quotes of the Day

It was dusk when the first fireball burst from the Mekong. A glowing pink orb hovered over the chocolaty waters for a split second then accelerated noiselessly skyward, winking out some 100 meters above. Minutes later, another soared from the roiling river. Then some way downstream, a string of four burst into a bruised sky that was looking angrier by the moment. Each tiny eruption was greeted with a jubilant roar, like a kickboxing crowd hailing a series of withering knee strikes. The lights looked a bit like exploding flares, though there was no hiss or smoke, no sparkling arc back to earth. To a cynic like myself, they looked indisputably man-made. But to the believers—gathered in the tens of thousands along the riverbank—this was the breath of the Naga, the mythical serpent of Buddhist lore that many Thais believe haunts the broad reaches of the Mekong in Nong Khai province.

Locals know the phenomenon as bung fai paya nak (Naga fireballs), which have been bubbling up from the mighty river on the late autumn night of the full moon at the end of the Buddhist Lent for as long as anyone can remember. "I've seen them since I was a little girl," says Pang Butamee, 70, who lives in a flood-prone hut on the river's edge. Nearby is Wat Paa Luang—an elegant, 450-year-old temple and one of the most popular spots to watch the fireballs. "I've seen them come up from the river, and also from canals and dams," she claims. "My mother and father saw them, and their mothers and fathers. And I've seen the Naga too. It was like a huge, silver snake swimming down the river. I saw it when I was 13 years old."

Nong Khai's Naga has become the Mekong's Loch Ness monster. In this sleepy province in the heart of the Isaan region 620 kilometers northeast of Bangkok, where men are men and bugs are food, just about everyone is happy to regale you with tales of monster sightings or giant, snaking tracks left in the riverbank's mud. Some locals brandish grainy pictures of what could be anything from a log to a boat, and swear it is evidence of the outsize serpent. And then there's that postcard: ubiquitous and eye-catching, of a band of U.S. service members purportedly stationed in the area in the early 1970s, staggering under the weight of an eight-meter-long, silvery, eellike fish. Locals swear it's genuine, and say all of the men in the photo met with messy ends. One oft told story holds that the fish itself disappeared on its way to America for scientific study.

If the fireballs, however, are a hoax, it is one conceived and perpetuated on a grand scale. According to Phrakhru Pichai Kitjaton, abbot of Wat Paa Luang, the temple houses written records of monks witnessing fireballs hundreds of years ago. And each year, anything from 200 to 800 of the fiery orbs are sighted along a 100-kilometer stretch of the river. "Are they real? Does it matter? Faith is the thing," he says, with a Mona Lisa smile.

One man not prepared to take the fireballs on faith is Nong Khai doctor and self-taught cosmographer Manas Kanoksin, who has spent 11 years trying to prove his theory that the fireballs are a natural phenomenon caused by pockets of methane bubbling up from the riverbed.

With mad-scientist intensity, he deluges me with data and baffles me with charts for hours. His hypothesis is that the Buddhist Lent full moon coincides with the period when the earth is passing closest to the sun. The sun's pull of gravity, he says, combined with a higher degree of UV radiation increases the concentration and volatility of oxygen at ground level that could cause existing methane escaping from the riverbed to spontaneously ignite. "In fact, it's not only one night per year," he insists. "The fireballs occur over several nights in October, and again in May when the earth swings closest to the sun again."

"Am I obsessed? Maybe," says the doctor, "but I am absolutely convinced that my theory is correct. If the fireballs are fake, the hoaxers would have to be more than 100 years old for a start. They'd have to be able to navigate a dangerous river in the dark, dodge the Thai and Lao patrol boats, and be incredibly good at keeping a secret."

Dr. Manas' principal detractor is Professor Montri Boonsaneur, who teaches geological technology at Khon Kaen University and was in charge of an underwater survey prior to construction of the nearby Thai-Lao Friendship Bridge. He says it's impossible that bubbles of methane could form in the river's rocky bed or survive its turbulent flow." I don't want to say the fireballs are man-made, but they're definitely not natural," he says.

The pair have engaged in a series of fiery debates on the topic, and their rivalry is a source of amusement for locals—most of whom are content to believe in the phenomenon's supernatural provenance. Next year, new combatants will enter the fray. Scientists from Bangkok's King Mongkut University of Technology Thonburi say they plan to settle the mystery once and for all. They have developed a submarine robot capable of probing the river's depths and reporting back to a land-based control center. But "some things are better left alone," warns Pang, the 70-year-old riverbank resident. "Don't try to put the Naga to the test. He will become angry."

She might be right. Within 15 minutes of my first fireball sighting, thunderhead clouds that had been threatening ominously suddenly bore down with full force. The heavens opened, and fierce gusts of wind turned the rain horizontal. At Wat Paa Luang, the fireballs were forgotten in the stampede for shelter. A soaked mass of humanity huddled under flapping tents, as the booms and bangs and drawn-out rumbles of the tempest sounded more and more like the admonitions of an irate demigod.

• Jason Gagliardi
• Thailand's Mekong Nessie Leaves a Hot Trail