In a rainforest in the heart of Amazonian Peru, scientists believe they have discovered the world’s largest thermal river, running hot for nearly four miles and reaching up to 80 feet at its widest point and 16 feet at its deepest.

While the river’s extreme temperatures are not unusual for a geothermal surface, it is deemed remarkable in that it is non-volcanic. The nearest active volcanic area is actually more than 430 miles (700km) away.

The so-called ‘Boiling River’ is said to be the “crown jewel” of an unusual collection of three non-volcanic rivers in the area which also include the Salt River (a salty thermal stream) and the Hot River (a thermal freshwater stream) - both much smaller in comparison to the Boiling River.

A shaman (healer) standing by the Boiling River Credit: Devlin Gandy/The Boiling River Project

Fed by both boiling and near-boiling hot springs, the river also feeds several thermal waterfalls along its length, the most impressive of which has a 20ft-drop into a large thermal pool, the Boiling River Project, which is investigating the phenomenon, reports.

Some parts of the river are said to be so hot that various animals that have fallen into it have boiled instantly, according to geoscientist Andrés Ruzo who discovered the river and leads the project.

A picture of a frog that has been boiled alive in the Boiling River Credit: Andrés Ruzo/The Boiling River Project

“The first thing to go are the eyes. Eyes, apparently, cook very quickly. They turn this milky-white color. The stream is carrying them," he said.

"They're trying to swim out, but their meat is cooking on the bone because it's so hot. So they're losing power, losing power, until finally they get to a point where hot water goes into their mouths and they cook from the inside out."

Members of the Santuario Huistin healing community in the Amazonian region of Peru Credit: The Boiling River Project/Facebook

Though what’s believed to be the river’s ancient name, Shanay-timpishka, translates to ‘boiled with the heat of the sun’, “the river boils because of fault-fed hot springs”, Mr Ruzo revealed in a TED (Technology, Entertainment, Design) conference seminar in 2014, which was released on Ted.com this month.

“As we have blood running through our veins and arteries, so too, the Earth has hot water running through its cracks and faults.

“Where these arteries come to the surface, these earth arteries, we'll get geothermal manifestations: fumaroles, hot springs and in our case, the boiling river” he said.

The PhD student in geophysics at Southern Methodist University in Dallas,Texas, first heard about the river several years ago from his father who shared a story about Spanish conquistadors encountering a mysterious terrifying river that boils from below while they were attempting to kill the last Inca emperor.

The Boiling River set in an Amazonian rainforest in Peru Credit: The Boiling River Project/Facebook

The river came up in conversation again, years later, from his aunt who claimed she’d seen this river before and even swam in it. Curious to get to the bottom of its existence, in 2011 he went on a hike, led by his aunt, through the jungle where it was said to be found, and was amazed to see the legendary river with his own eyes.

“At a time when everything seems mapped, measured and understood, this river challenges what we think we know,” he said at the TED conference.

“It has forced me to question the line between known and unknown, ancient and modern, scientific and spiritual. It is a reminder that there are still great wonders to be discovered.”

Maestro Juan Flores runs the Mayantuyacu healing centre in Peru Credit: Devlin Gandy/The Boiling River Project

Since his discovery, Mr Ruzo launched the Boiling River Project for the research and protection of the river and its surrounding area, including its rich and diverse plant and wildlife, which preliminary studies have indicated are found in the jungles along the river.

Shrouded with layers of legends, spirituality and mysticism, the Boiling River is considered a sacred place to its local community.

The river area is also home to the Santuario Huistin and the Mayantuyacu, two native Amazonian healing communities, who have long considered it a sacred site and place of spiritual powers that only the most powerful community healers would visit “to commune with the spirits” and learn about the secret healing powers and rituals of their predecessors.

Andrés Ruzo speaking about the Boiling River at the TED conference Credit: Ted.com

The greatest threat facing the river area currently is deforestation, which could lead to it vanishing completely if protective measures aren’t in place, Mr Ruzo believes.

One of the goals of the project is to have the Boiling River declared a Peruvian national monument and have its remaining jungle be legally designated for the exclusive use of ecological activities, including conservation and ecotourism, and ultimately promote “responsible tourism that aims to respect and appreciate the local culture, as well as protect the jungle”.

Tourists wishing to visit the river are recommended to liaise directly with either Mayantuyacu ( mayantuyacu.com ) or Santuario Huistín ( santuariohealing.com ) centres, both of which have a long history of receiving tourists and providing visitors with detailed travel tips, safety advice and warnings about the inherent potential dangers of visiting the river, which is “hot enough to give serious second to third degree burns in seconds”, according to the project.

While “the overwhelming majority of people who visit the area have safe and unforgettable visits, without harmful incidents”, these trips may "not be suitable for everyone given the difficulty of access and rural conditions," the website of the project warns.

“Prepare for very hot (both from the sun and the river) and humid conditions, lots of hiking, bug bites, no air conditioning, no internet or mobile reception, as well as being about an hour away from the nearest clinic, and at least three hours from the nearest hospital (in Pucallpa)."

“Your personal safety is entirely your own responsibility and when you enter this jungle you do so at your own risk. There are no boardwalks, no ropes, and no handrails. The Boiling River area remains (for the most part), wild and untamed— and we hope to keep it this way” it said.