The Amazon’s legendary Boiling River

As a boy in Peru, Andrés Ruzo heard the legend of the Boiling River from his grandfather. Later, as a Ph.D. candidate studying geothermal science, Ruzo began to wonder: did the river actually exist? This question led him to the river in the Amazon rainforest, where he began a research project that would inspire millions. Throughout his research, Ruzo has relied on Xylem's YSI handheld meters to sample the river's water quality, gathering data that provides new insights into the phenomenon.

The story Ruzo's grandfather told him of the Boiling River dates back to the time of the conquistadors. The Incas made up a story about a city made of gold, El Dorado, deep in the rainforest. When surviving gold seekers staggered back, they described the eternal night of the dark rainforest, shadowy depths guarded by silent warriors with poison-tipped arrows, spiders big enough to devour birds, clouds of insects, and a river that could boil a man alive.

Later, as a Ph.D. candidate at Southern Methodist University (SMU) studying geothermal science, Ruzo recalled his grandfather's tale. A map of thermal springs in Peru made him wonder if a boiling river could actually exist in the Amazon forest. Scientists and oil prospectors told him it wasn't likely, but when he asked his aunt, she said, "I've been there." In fact, his aunt showed him the way to the river's steamy banks.

Asháninka shaman Maestro Juan Flores. Photo credit: Sofía Ruzo.

A sacred river and a threatened ecosystem

After visiting the legendary river, Ruzo felt a newfound urgency to spread awareness about it. The forest around the river was still patrolled by bird-eating spiders, native shamans, wasps, and mosquitoes. But also, lumber traffickers and illegal squatters who contributed to the forest shrinking. He witnessed clearcuts and burned stumps spread across the landscape around the Boiling River. Ruzo was in a race against the chainsaws and torches that threatened the river and its ecosystem.

"Imagine being in this beautiful, cool, twilight world of the forest and suddenly opening up and stepping out into a totally deforested, apocalyptic landscape with massive tree trunks as big as your car - trees that you knew," he says, describing a trip back to the Boiling River through newly cleared land. "You go to the greatest celebration of life on the planet, and you see it go silent."

Andrés Ruzo at the Boiling River. Photo credit: Devlin Gandy.

Ruzo's mission to raise awareness and protect the river

After that harrowing trip, Ruzo put his dissertation research on the back burner and dedicated himself to telling the story of the Boiling River to the wider public. He wrote a book about their journey to the Boiling River, an expedition funded by a National Geographic Explorer grant. He gave a TED Talk that has logged more than 2.4 million views, and he has been interviewed countless times about his scientific discovery of a river that the members of the local Amazonian tribes have held sacred for generations.

Ruzo used science to make the case for protecting the area around the Boiling River and became an advocate for land rights for the people who ancestrally call this jungle home, including the Asháninka and Shipibo tribes. The Asháninka call the Boiling River "Shanay-timpishka" - meaning "boiled by the heat of the sun."

"There is a moral obligation to science," Ruzo says. "I learned to be a scientist from Western thought - that's how I was trained," he explains. "But my seeds of conservation working in the Amazon came from Maestro Antonio Muñoz, a Shipibo leader. He opened my eyes and said, 'You're here. You're documenting everything. Is that enough for you? Is just documenting the destruction enough?'"

Before he published the data for fellow researchers, Ruzo promised himself he would help protect the landscape. He spent years raising awareness of the river and its magic, and helped indigenous leaders obtain the legal rights to their land. Now that the land belongs to the indigenous residents, Ruzo has turned back to publishing his data.

Measuring the path and temperatures of the Boiling River

The Boiling River starts as a cold, small jungle stream that grows significantly in volume and temperature as it flows over geologic fault zones. With dozens of hot springs and a powerful flow rate, the Boiling River in Peru's Amazonian rainforest is the largest documented thermal river in the world.

For over 6 kilometers (about 4 miles), the river weaves through rocks, dense jungle, and thermal mudflats, widening to a peak of about 30 meters (100 feet) and hitting a maximum depth of almost 4.5 meters (15 feet).

Along the way, Ruzo has measured temperatures ranging from the ambient air temperatures of around 27 °C (80 °F) to steaming stretches bubbling at average temperatures around 90 °C (194 °F). Major stretches of the thermal portion of the river far exceed 47 °C (116 °F), a life-threatening temperature if something falls in.

At sea level, water boils at 100 °C (212 °F). At La Bomba, an aggressively bubbling hot spring, whose name translates to "the Pump", Ruzo measured the river's temperature at 94 to 97 °C (201 to 207 °F). About 300 meters (1,000 feet) downstream of La Bomba, the river's water temperature peaked at a spring reaching 99.1 °C (210 °F).

Ruzo using a thermal camera at the river. Photo credit: Sofía Ruzo.

Researching the river's unusually clean water

Two of the biggest mysteries of the river are the source of its hot water and its purity. The Asháninka believed Shanay-timpishka was the work of powerful spirits. After all, the water is remarkably safe to drink, unlike most other local water sources that often plague drinkers with dysentery, Legionnaires' disease, and other diseases.

"You could understand why the indigenous people would say, 'This is the work of powerful spirits because it's healthy water. This was put here to heal us.'"

Ruzo uses a YSI Pro Series handheld meter to test pH, oxidation-reduction potential, and electrical conductivity for clues on the river's path deep into the earth and back. He also uses the instrument to measure the water from different inflow points along the river and monitor changes over time.

"I've worked on geothermal systems all over the world, and you wouldn't want to drink most of these waters," Ruzo says. "They can be full of heavy metals, be highly acidic or alkaline, or even harbor things like 'brain-eating amoebas.' In the case of the Boiling River, there was effectively nothing in the water. Using my YSI, I found the Boiling River's waters were 'cleaner' - i.e., lower electrical conductivity - than Evian."

Ruzo was introduced to YSI's handheld meters at SMU by renowned water quality researcher Dr. Andrew Quicksall and quickly realized how important one would be for his own studies.

"Dr. Quicksall's class showed me how the pH, electrical conductivity, redox potential, and other parameters all come together to help understand what kind of environment that water is in," Ruzo explains. "It made the invisible visible in a way I thought was really powerful."

The source of the Boiling River's hot water

The Boiling River is 700 kilometers (430 miles) from the nearest active volcano, so scientists do not believe that the river's hot water is caused by a volcanic system. The Earth's hot crust, however, is the likely answer. This is supported by the purity of the water, geochemical and geophysical data, geologic models and other research.

Ruzo believes the Boiling River is fed by water that dives deep into the Earth, gets heated by the surrounding rock, and is propelled by heat and pressure back through faults to the surface.

Ruzo has introduced the Boiling River to an estimated 800 million people around the world through his outreach efforts. Despite increased awareness, the Boiling River and the land around it remain in the "reddest" of Peru's deforestation red zones. However, the local community now legally own the land and the river is listed as a conservation priority for Peruvian conservation groups. Through Ruzo's efforts to uncover what was once a legend, the Boiling River is now the center of an active conservation campaign calling for government protection.

Read the full story and more in Mission: Water magazine.

Written by Steve Werblow
Top image photo credit: Delvin Gandy

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