It begins high in the Peruvian Andes as a thin sheet of crystal water flowing down the side of a rock wall. By the time its journey ends in the Atlantic Ocean some 3,900 miles (6,275 kilometers) away, it has become the world’s largest river by volume and possibly the longest: the mighty Amazon. SEE MAP.

Long the subject of argument and speculation, the precise location of the source of the Amazon has been pinpointed by a five-nation National Geographic Society expedition using cutting-edge Global Positioning System (GPS) navigational equipment. The team, headed by 46-year-old Carmel, N.Y. math teacher Andrew Pietowski, has identified the place where it begins on a slope of Nevado Mismi—a 18,363-foot-high (5,597-meter) mountain in southern Peru.

Expedition leader Andrew Pietowski of Carmel, New York, pauses in the snow of Peru’s Nevado Mismi to gauge his position with high-accuracy Global Positioning System equipment. Pietowski led a 22-person team representing five countries that put the technology to work to find the exact source of the Amazon River. Photograph by Jacek Bogucki

“It’s a pretty spot, especially in the afternoon when the sun is lighting the snow higher up on the mountain,” says Pietowski of the place where the Amazon starts its winding journey through a grass- and moss-covered alpine valley, to be joined by other streams and rivers on its journey to the sea.

“You’re standing in a green valley at the base of a really impressive, almost black cliff about 40 meters (130 feet) high. On top you see the shape of the mountains covered with snow, contrasting with the dark blue sky at this altitude. It is very silent and serene. I felt great standing there, this incredible beauty permeating me. I was part of the landscape, the ice, the rocks, everything.”

That the Amazon springs from the Andes’ high glacial regions has been known for centuries. Jesuit Cristoval de Acuna described his theory as to its source to the king of Spain in 1641. But identifying the particular peak where it is born has long baffled explorers and scientists.

EARLIER EXPEDITION

Geographer Andrew Johnston from the Smithsonian Institution's National Air and Space Museum walks along Lake McIntyre on a Peruvian mountain known as Nevado Mismi, recording information on his precise location using Global Positioning System equipment. An expedition sponsored by the National Geographic Society employed high-accuracy GPS to determine the source of the Amazon River. The expedition's finding: Nevado Mismi. Photograph by Zbigniew Bzdak

In 1971 a National Geographic expedition led by explorer-journalist Loren McIntyre identified Nevado Mismi as the source. That conclusion has been the basis for National Geographic maps of the region ever since. However, without precise instruments, verification has proved elusive. In recent years at least one other stream flowing from a different mountain has been in contention.

“I asked Loren, how did you know?” said Pietowski. “He said he was very lucky and he had very strong intuition. He said the mountain was calling to him.”

The person in charge of the instruments that nailed it was geographer Andrew Johnston of the Smithsonian Institution’s National Air and Space Museum in Washington. The source of the river, he says, can be defined as the most distant point in the drainage basin from which water runs year-around, or the furthest point from which water could possibly flow into the ocean.

“Nevado Mismi fits both these definitions,” says Johnston.

The team consisted of 22 people representing the United States, Peru, Canada, Spain, and Poland—where Pietowski was born. They explored all five of the remote Andean rivers that combine to form the Amazon: the Apurimac, Huallaga, Mantaro, Maranion and Urubamba-Vilcanota.

Traveling by foot, Jeep, bicycle, and horseback, the expedition worked from a base station near the confluence of several tributaries of the Apurimac River. They used GPS gear to map the path of the Continental Divide—the boundary of the Amazon River drainage basin—and to map the area’s drainage features. Their instruments are accurate within a range of 1-5 meters (3-6 feet).

FASTER BY MOUNTAIN BIKE

“It took six or seven hours of trekking with backpacks every day from the base camp to go to the work place,” said Pietowski. “Sometimes I used a mountain bike and it took only an hour and twenty minutes. Either way, at 5,300 meters (17,400 feet), believe me, it’s not fun. The tent was frozen white in the morning, like it had a shell on it.”

Besides the cold and high altitudes, the team endured vicious winds and rough terrain, according to Pietowski. “I saw my face on video a week ago. If I hadn’t had on my National Geographic baseball cap, I wouldn’t have known it was me. I looked very old, swollen, tired, just like everybody else.”

The final expedition was a culmination of four reconnaissance trips in 1998 and 1999 led by Ned Strong of Lexington, Massachusetts, Pietowski, and Johnston. Another team member, Piotr Chmielinski, originally of Poland, was the first person to navigate the entire length of the Amazon, and led a 1991 expedition through Peru’s Colca Canyon near the Amazon.

Pietowski, who with his family fled political unrest in Poland in 1979, lived in Peru for three years before coming to the United States. He first became interested in Nevado Mismi when he saw it while leading a group of kayakers from Poland into the area in 1981.

He has been hooked on adventure and exploration since childhood.

“You have to have it in your genes,” he says. “You have to want to know what is behind the horizon line. For the Amazon, if there is a mouth of the river, there must be a beginning. I wanted to know where it was.”