What's the longest river in the world, the Nile or the Amazon? The question has fueled a heated debate for years. Now, an expedition into the South American jungle aims to settle it for good.
Using boats run on solar energy and pedal power, an international team of explorers plans to set off in April 2024 to the source of the Amazon in the Peruvian Andes, then travel nearly 7,000 kilometers (4,350 miles) across Colombia and Brazil, to the massive river's mouth on the Atlantic.
"The main objective is to map the river and document the biodiversity" of the surrounding ecosystems, the project's coordinator, Brazilian explorer Yuri Sanada, told AFP.
The team also plans to make a documentary on the expedition.
Around 10 people are known to have traveled the full length of the Amazon in the past, but none have done it with those objectives, says Sanada, who runs film production company Aventuras (Adventures) with his wife, Vera.
The Amazon, the pulsing aorta of the world's biggest rainforest, has long been recognized as the largest river in the world by volume, discharging more than the Nile, the Yangtze and the Mississippi combined.
But there is a decades-old geographical dispute over whether it or the Nile is longer, made murkier by methodological issues and a lack of consensus on a very basic question: where the Amazon starts and ends.
The Guinness Book of World Records awards the title to the African river.
But "which is the longer is more a matter of definition than simple measurement," it adds in a note.
The Encyclopedia Britannica gives the length of the Nile as 6,650 kilometers (4,132 miles), to 6,400 kilometers (3,977 miles) for the Amazon, measuring the latter from the headwaters of the Apurimac river in southern Peru.
In 2014, US neuroscientist and explorer James "Rocky" Contos developed an alternative theory, putting the source of the Amazon farther away, at the Mantaro river in northern Peru.
If accepted, that would mean the Amazon "is actually 77 kilometers longer than what geographers had thought previously," he told AFP.
- Rafts, horses, solar canoes -
Sanada's expedition will trace both the Apurimac and Mantaro sources.
One group, guided by Contos, will travel down the Mantaro by white-water rafting. The other will travel the banks of the Apurimac on horseback with French explorer Celine Cousteau, granddaughter of legendary oceanographer Jacques Cousteau.
At the point where the rivers converge, Sanada and two other explorers will embark on the longest leg of the journey, traveling in three custom-made, motorized canoes powered by solar panels and pedals, equipped with a sensor to measure distance.
"We'll be able to make a much more precise measurement," Sanada says.
The explorers plan to transfer the sustainable motor technology to local Indigenous groups, he adds.
The expedition is backed by international groups including The Explorers Club and the Harvard map collection.
- Worse things than snakes -
The adventurers will traverse terrain inhabited by anacondas, alligators and jaguars -- but none of that scares Sanada, he says.
"I'm most afraid of drug traffickers and illegal miners," he says.
The boats will be outfitted with a bulletproof cabin, and the team is negotiating with authorities to obtain an armed escort for the most dangerous zones.
If the expedition is successful, it may be replicated on the Nile.
Sanada says the debate on the world's longest river may never be settled. But he is glad the "race" is drawing attention to the Amazon rainforest's natural riches and the need to protect it as one of the planet's key buffers against climate change.
"The Amazon is (here), but the consequences of destroying it and the duty to preserve it are everyone's," he says.
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