Near the top of a mountain in the Peruvian Andes is a small lake named Laguna McIntyre. This is the source of the Amazon River, so named for the National Geographic photographer, writer, and prolific explorer who made the discovery. “Amazing is the word heard most often at National Geographic headquarters to describe Loren McIntyre, who surmounts all obstacles with ease,” read a 1987 editor’s note marking his 70th birthday.

But there was one adventure McIntyre rarely spoke about. In the late 1960s, he went to Brazil in search of an uncontacted tribe in the Amazon rain forest called the Mayoruna. McIntyre was dropped off on a riverbank, and followed the tribe into the forest. Before long he was unable to find his way back and ended up missing his return flight. McIntyre lived with the tribe for two months. Although they shared no common language, he discovered he could communicate with the chief via telepathy, in a manner he began to call “beaming.” This skill, he later learned, was known to the tribe as the “other language,” a way of communicating possessed only by the elders.

View Images In this McIntyre photo, Txukahamẽi Indians clear the forest for a new settlement. Seven members of the group died while fighting over whether to move to a new upriver site, as ordered by the government, or to stay and resist. They eventually relocated. Photograph by Loren McIntyre, National Geographic

The Mayoruna were on the run, moving deeper into the forest to escape encroaching developers and settlers. As McIntyre followed them, they began to destroy their possessions in a quest to return to “the beginning,” a time before outside civilization intruded into their lands. One night, in the midst of these preparations, a tributary flooded their camp, and McIntyre grabbed onto a drifting balsa raft. He floated down the river and was rescued by a pilot.

If it sounds too good to be true, the New York Times thought so as well. In 1991 McIntyre’s story was published in a book called Amazon Beaming by Petru Popescu. They’d met on a trip to the basin, where McIntyre confided in him, telling him about his strange experience 16 years earlier. It was, McIntyre later said, the first time he’d told anyone. The Times book reviewer skeptically lists the events that left McIntyre stumbling out of the jungle with one ruined roll of film and no notebooks, but a conviction that he’d communicated with his mind. The writer says he was “tempted to dismiss this story as the work of somebody angling for a contract with Steven Spielberg.” Then he observes: “But Loren McIntyre, a veteran National Geographic photographer and journalist widely respected for his eye, his prose, and his careful observation, is not one to tell tall tales; and truth can be stranger than fiction.”

Amazon Basin SOUTH AMERICA ATLANTIC OCEAN Venezuela Guyana Colombia Ecua. Brazil Peru Amazon Basin Bolivia 500 mi Laguna McIntyre 500 km NG MAPS The Amazon and its tributaries Brown water Black water Blue water

McIntyre moved to Latin America after a stint in the Navy during World War II, working for the U.S. Agency for International Development and as a filmmaker, until he started to write for National Geographic in the 1960s. For years, McIntyre, who considered himself as much scientist as journalist, kept his unusual experience secret. "I'm pretty reluctant to voice very much about the beaming experience because I didn't want my friends to think I'd gone around the bend. 'What is this? The guy's hallucinating?'” he later told the Los Angeles Times.

This fall, Popescu’s book debuted in its newest form, a one-man Broadway play called The Encounter. Simon McBurney, a Brit who’s made his name in pushing the boundaries of traditional theater, wrote, directed, and stars in it. In his quest to understand consciousness, he’d read Popescu’s book in the ’90s, and he felt drawn again and again to McIntyre’s story. “It’s the last great unsolved mystery—the one we carry inside our heads,” McBurney says in an interview. He was fascinated by the white Western explorer who became so immersed in another culture that he began to experience something that so defied logic.

In the play, McBurney is both himself and McIntyre. Despite the bare stage and lone actor, the audio-centric show develops so many layers it becomes hard to differentiate past and present, reality and illusion. Headphones provide full immersion into the sounds of the Amazon rain forest, and, as McBurney describes it, “You begin to see things that are not there.”

Discovering the Source

In the archives of National Geographic headquarters in Washington, D.C., are thousands of files from the magazine’s 128-year history. Each story, until the 1990s, had its own manila folder, filled with telegrams, itineraries, and letters. The file for the Amazon River story chronicles a 20-year effort to tackle the daunting subject, beginning with a 1952 Washington Post clipping about the river’s development and an editor’s recommendation to send a photographer to cover it.

View Images Simon McBurney plays Loren McIntyre in his one-man show, The Encounter. The audio-heavy performance distorts the audience's sense of time and space. Photograph by Sara Krulwich, The New York Times/Redux

The story continued to surface over the next decade, and in the 1960s McIntyre sent multiple letters to the board proposing to shoot the assignment. “When I was a seventh-grader the first short story I ever tried to write opened with a gunfight on the Amazon,” he wrote in one pitch. “I steered a blue-water steamship into O Rio Mar, The River Sea, in July 1935, navigated its upper reaches on a Peruvian gunboat in 1953, and last canoed on the headwaters in October 1966. I’ve shot nine films there. My stack of Amazon lore continues to grow.”

That summer a husband-wife expedition had pinpointed a mountain stream in Peru called the Huaraco as the source of the Amazon. But McIntyre was dubious; he believed that the original tributary was farther south, and he called the National Geographic cartography department to argue his point.

In 1969, just a few weeks after McIntyre emerged from his encounter in the jungle, he again sent a pitch to his editor. He proposed to trace the river’s different rain forest tributaries—the brown waters of the west, the black waters of the north, and the blue waters of the south—and find the source. “The Magazine has never published a story on the whole Amazon, just bits and pieces from time to time,” he noted. “The article remains to be done. I want to do it.”

A year later, in October 1970, his name shows up on an assignment sheet for upcoming stories, which spanned topics from Tasmania to the adobe city of Chan Chan in Peru. Next to Amazon it says, “See if McIntyre can do.”

The next year he was offered the assignment, but the editors were nervous. “Mr. McIntyre’s plans were too ambitious” read a story meeting memo. He was asked to limit the trip to 20 destinations and 100 days. On September 20, 1971, he was on his way, exploring the Amazon’s host countries. His itinerary notes without fanfare that the plan for October 13 was to “climb to Amazon source.”

It took him two more days, but then, looking down from the peak of a mountain called Nevado Mismi, he saw a small lake that fed into a brook, and eventually, he knew, turned into the Amazon River.

View Images This view of the Rio Negro, the Amazon's largest tributary, was taken by McIntyre from near the city of Manaus in Brazil. Photograph by Loren McIntyre, National Geographic

The saved correspondence doesn’t show McIntyre’s reaction to the discovery, but a few months in, McIntyre wrote to his photo editor about a particularly dangerous expedition he planned to undertake in the blue water region and asked that the letter not be shared with his wife. A month later he emerged from the 6,500-mile, 44-stop journey. “[I]t was probably the first time anyone has dared such a journey in an overloaded Cessna 182 w/o radio, w/o filing flight plans, and w/o announcing arrivals or departures,” he wrote.

Throughout the journey he wrote of a deeply held fear that the indigenous populations he was meeting had little chance of survival against Brazil’s plans for the Amazon. “No concern for the Indian is great enough to withstand the current surge of a hundred million people and a hundred billion expansionist dollars and a vast governmental program of ‘integrar ou entregar’ [integrate or deliver] which you gotta see to believe,” he says. “Besides, no one knows what’s best for the Indian. There are dozens of angry yet well-meaning points of view. Almost all ... admit that there seem to be only two final solutions: eventual absorption into prevalent Brazilian national life, or death.” Today, there are at least a hundred uncontacted groups still living in the Brazilian rain forest, and their land remains threatened by the development McIntyre observed a half century ago.

When he filed a story draft months later, his editor reached out to four colleagues for help trimming it by 20 pages. “His trouble seems to be too rich a wealth of background, knowledge and experience,” one wrote.

View Images McIntyre's story on the cover of the October 1972 National Geographic. Cover photograph by Loren McIntyre, National Geographic

“The Amazon—Mightiest of Rivers” proclaimed the cover of National Geographic in October 1972. In the story, McIntyre reported that a miniscule lake 17,400 feet up in the Peruvian Andes sends a stream of water nearly 4,000 miles to the Atlantic Ocean and is “the farthermost source of the Amazon yet discovered.” Explorers of the Nile and Amazon Rivers have long debated which was longer. McIntyre’s expedition placed the Amazon at 4,000 miles to the Nile’s 4,160 miles. The competition between the two continues today, but the Nile is generally considered to be longer.

The origin point was renamed Laguna McIntyre. For years his claim that the lake was the source was disputed, and other potential sources were identified. In 2001 the magazine published an update: A 22-person crew using 40,000 GPS readings concluded that “a drop of water from Lake McIntyre flows 4,000 miles to the Atlantic.”

The team was incredulous that McIntyre had found the river’s source with just a small team and little technological support. “I asked Loren, how did you know?” said team leader Andrew Pietowski, a math teacher and South America explorer. “He said he was very lucky and he had very strong intuition. He said the mountain was calling to him.”

Recalling the Explorer

McIntyre died in 2003 and there are few left at National Geographic who remember the days when he would return to his home in Arlington, Virginia, and visit the magazine offices with stories and film from the jungle.

“He was always getting into trouble when he was away because he took such chances and his adventures were so wild,” says former senior photo editor Susan Welchman. She was working with McIntyre when he disappeared again in 1982. This time his captors were Venezuelan police, who took issue with his documentation and threw him in a detention cell. She recalls him telling her that he’d saved his film by convincing them it hadn’t been shot, then licked the red coating off some pills so he could urinate red and convince them he was deathly ill.

“Loren was the most renowned amongst us editors and photographers,” she says. “His entire life was dedicated to this kind of travel and documenting. He liked communicating with people he didn’t share any part of life with.”

Few contributors to National Geographic have managed to pull off both writing and photographing a story, but McIntyre was unusual—often out of necessity. “In Loren’s case, when he’d get himself someplace, he couldn’t get someone else there,” Welchman says. She recalls him being such a conservative photographer that he would strive to shoot a whole story on one roll of film with one lens. “To paint a picture with this guy is almost impossible. He always had close calls with snakes and poison arrows,” she says, recalling him as a “skinny, tall, birdlike man who talked endlessly in a rumble.”

He continued photographing in Latin America, but never forgot his experience with the Mayoruna. "I wasn’t sure myself if it had really happened or not,” he told the Seattle Times in the ’90s. “Hallucinations are something that happen to many explorers and to all mountain climbers."

Doubtful of his own memories, he’d tracked down what was left of the tribe in the late 1970s. One community had moved deeper into the jungle, while another had moved out of the forest. He recognized one of the men in the integrated community from his first encounter. He asked if the “old language,” the beaming he remembered, was still used.