Geologically, Lake Tele is a small mystery. It formed in Pliocene alluvial sediments by a process that has never been fully explained, leaving an elliptical, nearly circular basin in the heart of the swamp. Strangely, it has no significant rivers feeding it and none draining it, sitting instead like water held in a cupped hand. The lake itself is turbid and rich in decaying organic matter, its water so acidic that its pH drops below four, more sour than vinegar. The Likouala-aux-Herbes swamp forests that surround it press in from every side and are gradually covering the lake over. This is not a place that gives up its secrets easily, and the dense, waterlogged forest around it remains one of the least surveyed environments in Central Africa.

In the folklore of the peoples who live along the Likouala, Lake Tele is the best-known haunt of the Mokele-mbembe, described as a large, long-necked, reptilian creature. The most famous tale tells how, around 1959, members of the local Bangombe community built a barrier of sharpened stakes across a tributary to keep the creature from disturbing their fishing. The story holds that a Mokele-mbembe forced through the spikes, was wounded, and was killed by the villagers. It is a vivid piece of oral tradition, and it should be understood as exactly that: a story, told and retold, with no physical evidence behind it. To the communities here, such accounts are part of a living relationship with a vast and genuinely mysterious forest, woven into how this landscape is understood and passed down.

The legend has drawn a long parade of outsiders into the Likouala. Through the late twentieth century, expeditions of cryptozoologists and adventurers trekked to Lake Tele hoping to photograph a surviving dinosaur, gathering eyewitness accounts from village after village but never a shred of proof. The most literary account came from the British travel writer Redmond O'Hanlon, whose 1996 book Congo Journey describes his own arduous trek to the lake in search of the creature. The book is less a monster hunt than a richly observed portrait of the region: its plants and animals, the cultural practices of the people who guided him, and his encounters with the indigenous communities of the forest. The Mokele-mbembe never appears, of course. The mainstream scientific view is plain, that no evidence beyond testimony has ever surfaced, and the creature is regarded as folklore rather than fact.

The greatest surprise Lake Tele has produced is not a dinosaur but something almost as astonishing. The lake lies at the heart of the Lac Tele Community Reserve, a wetland of more than 4,300 square kilometres that has been a protected Ramsar site since June 1998. In 2006 and 2007, surveys by the Wildlife Conservation Society found that the swamp forests around the lake and the neighbouring dry forests were sheltering more than 100,000 western lowland gorillas, a population no one had known existed. At a time when the species was thought to be in steep decline, this hidden multitude was a genuine wonder. The forest that legend filled with monsters turned out to be hiding a real marvel all along, proof that the most remote corners of the planet can still astonish us.