In the middle of the great rapids at Samosierra, in the heart of northern Peru, the Marañón River makes a sudden right turn. More than 500,000 cubic meters of water per second slam into a cliff shaded by half-mile-high canyon walls, throwing up eight-foot waves that break hard over the rubber raft I'm in with three Peruvian guides. Their faces are grim. "When the river is high, hombre, it's bothered," Edgar Vicente, our captain, says. "Until it takes someone, it won't rest."
As fate would have it, the night before, a local fisherman got tangled in his net and drowned. Ever since, the water level has been dropping. The Samosierra is a Class IV now, scary but manageable. "Adelante, chicos, adelante," Vicente yells, urging us forward, and we pull hard, digging our oars into the waves. A hole opens beside the boat; I swing at empty air and feel myself falling before another wave catches the raft and knocks me back in. "Adelante!" The raft hits the new current around the bend, and we're through, laughing like madmen. "Look at it, boys," one guide says, whooping. "The mother to the greatest river in the world!" That night, as we pass around a bottle of pisco by our driftwood fire, under banana trees growing out of the rich muck of the last flood, I am haunted by the idea that the river is alive, willing to deal out life and death with the same hand.
The Marañón runs from the high snows of the Andes down to the jungle, where it forms a main source of the Amazon. For 400 miles, it slithers like a golden serpent — to borrow the name of a 1935 book about the river — through a vast canyon, often a half-mile deep, marked by Class III to Class V rapids and rustic farming villages.
Unfortunately for the region's inhabitants, the Marañón's narrow passages and high volume are also ideal for hydropower: The huge Brazilian construction company Odebrecht plans to build the Chadin 2 dam, part of a building craze that might result in some 20 dams on the Marañón in the next decade. If the dams are built, they will raise the water level more than 300 feet in places, drowning rapids and river towns alike, breaking the serpent's back with locks and reservoirs.
I am going down the last 200 miles of this route with a group of Peruvian and gringo guides led by Benjamin Webb, a 27-year-old Australian with blond dreads and a bone-dry deadpan. The trip is meant to be a sort of local hearts-and-minds campaign for whitewater rafting. In Peru, there is a long history of grassroots protests and rebellions stopping big-money mining and dam projects. Webb hopes to bring Lima kids and village kids alike down the river, putting badly needed money in the hands of valley organizations fighting the dams.
Over our two-and-a-half-week trip, we watch while the landscape changes with meditative slowness from high desert that looks like southern Utah down to what Peruvians call la ceja de la selva, "the eyebrow of the jungle." Ferns sprout among the cacti, and chattering green parrots appear in the mesquite trees. Above us rise high sandstone walls, their faults twisted almost vertically with the violence of the mountains' creation, rayed with the lines of hundred-year floods from cataclysms past.
Though locals have run the Marañón on balsa-wood rafts for centuries, the river is new to commercial rafting. In 2012, Rocky Contos, an American kayaker and explorer with a slate of solo first descents of rivers in Mexico, became the first person in a generation to run it. Since then, Contos has been working to open up commercial rafting along a 406-mile section of river, offering trips of one to five weeks down what he calls the Grand Canyon of the Amazon. "There just aren't many rivers where you can do an expedition this long," Contos explains in the market town of Bagua Chica, a few miles from the Marañón, before our trip. There are fewer every day: The Marañón dams are part of a worldwide rush to dam the last great wild rivers. The Yangtze is flooded, and plans are under way to dam the Blue Nile and to continue work on the Mekong as well. Contos ticks off rivers on his fingers. "If the Marañón goes, it would be like flooding the Sistine Chapel," he says.
The canyon is beautiful, but to Contos that is not what makes it special: It is special because it is wild. First, there is no official authoritative body along the river. Also, because the river is huge and undammed, it's the dominant force on the landscape, and it's an unpredictable one. "When you run a wild river, you just don't know what you're going to find," says Matt Primomo, a guide from Utah who is helping on this trip. He points downstream, toward a blind curve of Class III rapids. "We could come around that bend and find a huge landslide blocking the river. And then we'd just have to deal with it." This in a remote canyon, with no way to go but forward.
Among the river folk who farm the Marañón Valley, life beside the moody river has fostered a rugged and independent culture. We float through what feels like the old American frontier filtered through the tropics. It is populated by people whose families came, one woman explained to me, to escape highland estates — where "the landlords owned all the land and the crops and even your wife if he wanted her."
The ribereños — river people — tend fields of scrubby green coca and golden cacao under orange and mango trees. They live in fear of lake sirens and forest devils, panning for gold on the shores of a river capable of swallowing villages without a trace. In many of the Marañón towns, the men have formed peasant militias, called rondas, that keep out dam surveyors by force. "When we catch them, we discipline them physically," says Alvaro Huaman, a ronda member in the town of Tupen Grande, an oasis of bubbling creeks and fruit trees groaning with passion fruits, bananas, and mangoes. "I want my children to know that I did everything I could to protect this land."
The ronderos are tough men, mostly farmers, on war footing ready to protect their villages against destruction by the dams: In 2013, ronderos from the villages of Tupen and Mendan brought Rocky Contos before a village tribunal. The hearing ended in an alliance: Contos donated money, which went to buy the rondas' uniforms and trademark leather truncheons, and he negotiated the rights to keep bringing tourists in. This year the ronderos welcome us royally, offering tropical fruit I could not identify, and get us drunk on moonshine distilled from local cane. I fend off a push to hook me up with a sexy widow whose husband died six months before of tuberculosis. "You are under our protection," says Oscar Solano, the head of the Mendan ronda. "Nothing will happen to you here." But he suggests that it's a bad idea to show up without someone the locals know — like Contos or Webb — lest you be mistaken for a surveyor.
Finally, in the middle of June, following 17 days on the water, the Marañón carries us to our take-out at the Pongo de Rentema, where it joins two other rivers and doubles its flow. Below the Pongo, the river's character changes completely, its lines dissolving into a chaotic mess of whirlpools and culminating in an eddy the size of a football field swirling by the little town of El Muyo. As we surge toward land, trying to dock, the river spins the raft back like a stock car going around a track.
We struggle toward shore, fighting to free ourselves from the river's grip. The wonder of the wild Marañón, its aliveness and its terrible power, are all of a piece — and all conceal its vulnerability before the plans of civil engineers. If those men have their way, the river will become placid, safe, and dead. That force that carves through the tight canyon walls will be broken to the turning of turbines. As our raft crashes onto the smooth stones below El Muyo's wooden houses, the river surges on tranquilly behind us — all the while, in faraway capitals, men are plotting its doom.