In the green interior of Mohéli, tucked away in the forest of the Boundouni area, lies a rarity for a volcanic archipelago: a freshwater lake. Dziani Boundouni is a crater lake of greenish, sulphurous water, about thirty hectares in size, surrounded by tropical forest and home to herons and waterbirds. It is one of the few freshwater bodies in the Comoros and a wetland of international importance that has been protected for decades.
Getting there is part of the charm: a short walk through the island's inland forest, almost always with a local guide, until you look out over this flooded crater full of stillness, where the only sound is birdsong. In a country of sea, turtles and whales, Lake Boundouni shows the other side of Mohéli: its wooded, volcanic and silent interior, far less visited.
This guide tells you what you'll see, how to organise the trip from Fomboni or from the south coast, when to go and how to combine it with the Itsamia turtles and the Marine Park. A simple, low-impact outing, ideal for nature and bird lovers, in one of the quietest and most unusual corners of the archipelago.
Lake Dziani Boundouni is a volcanic crater lake, one of the rare freshwater bodies in the Comoros, formed by the geological activity that created Mohéli. Its greenish, sulphurous water and surrounding forest are home to waterbirds and valuable biodiversity, which led to its designation as a Ramsar site — a wetland of international importance — in 1995. Its history is that of the archipelago's volcanic geology and of Comorian efforts to protect their last wetlands; it is told on the history page.
Read the full history ↓The smallest, wildest and least populated island: birthplace of the accord that refounded the country and home to its first marine park, with green turtles, whales and living reefs.
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Origins, formation and what the sources say.
In a volcanic archipelago like the Comoros, a freshwater lake is a real rarity. Young volcanic islands tend to have porous rock that soaks up the rain, so the water seeps underground and hardly any permanent streams or lakes remain on the surface. That is why Lake Dziani Boundouni, in the interior of Mohéli, is such an exceptional sight: one of the very few stable bodies of fresh water in the whole country, and one of the most important.
The lake fills a volcanic crater, a depression formed by the geological activity that created Mohéli millions of years ago. It is essentially a maar, or explosion crater, that filled with water over time. Its roughly thirty hectares of surface have a distinctive greenish tint, owing to its high sulphur content and the processes taking place in its waters. Studies suggest that volcanic activity still persists underground beneath the lake, with springs that feed and renew it.
That volcanic origin and sulphurous make-up turn Dziani Boundouni into a one-of-a-kind lake, better for admiring than for swimming. Tucked into the forest of Mohéli's interior and surrounded by dense tropical vegetation, it creates a still landscape that contrasts with the marine abundance of the coast. It is proof that Mohéli, famous for its turtles and reefs, also holds treasures in its heartland, shaped by the same volcanic fire that raised the islands from the seabed.
The value of Lake Dziani Boundouni is not only geological but ecological. As a rare reservoir of fresh water in the middle of the ocean, it has become an oasis for wildlife, especially waterbirds. Herons, waders and other species visit its shores all year round, feeding in the wetland and finding shelter in the surrounding forest. For a small island like Mohéli, this freshwater ecosystem plays an outsized role in sustaining biodiversity.
That value was officially recognised in 1995, when the lake was designated a Ramsar site, that is, a wetland of international importance under the Ramsar Convention, which protects wetlands around the world. It was one of the first international recognitions of Comorian nature, and it put Dziani Boundouni on the map of natural areas worth conserving. The surrounding forest, known as the Boundouni forest, is part of that protected area, between the villages of Itsamia and Hamavouna in the south of the island.
Protecting this wetland is not a luxury but a necessity. On islands where fresh water is scarce, bodies of water like this one are both strategic and fragile resources, vulnerable to pollution, to deforestation of their catchment and to changes in rainfall patterns. Its conservation is part of the Comoros' wider efforts to preserve its natural heritage, the same efforts that led to the Mohéli Marine Park on the nearby coast. Land and sea, wetland and reef, are part of a single web of life that the island is trying to look after.
Lake Boundouni is a gateway to the interior of Mohéli, the least-known side of the wildest island in the Comoros. While the south coast draws travellers with its turtles, whales and islets, the heart of Mwali — mountainous, forested and sparsely populated — remains almost ignored by tourism. Yet that interior holds much of the island's land biodiversity: humid forests, endemic birds and habitat for Livingstone's fruit bat, the critically endangered giant bat found only on Mohéli and Anjouan.
For centuries, the interior was the domain of subsistence farming and of villages that lived off the land, alongside fishing on the coast. The Boundouni area, with its lake and forest, was part of that rural territory, prized for its water and for the resources of the bush. The walk visitors take today to reach the lake partly follows the paths the island's inhabitants used for generations to get around the interior.
Mohéli's forest, like those of the other islands, has suffered from clearing for firewood and crops, a serious problem in a poor and densely populated country. Conserving places like Boundouni also means protecting water, soil and the local climate, as well as wildlife. For travellers, heading into this forest to the crater lake means discovering a different Mohéli, quiet and green, and understanding that the island's natural wealth does not end at the water's edge.
Today, Lake Dziani Boundouni is a peaceful nature outing, far from the crowds — which, in a country like the Comoros, practically don't exist. There is no tourist infrastructure: you reach it on foot through the forest, almost always with a local guide, and the pleasure lies in taking in the flooded crater, watching the birds and listening to the silence of the island's interior. It is a low-impact outing, ideal for birdwatchers and lovers of unusual landscapes.
Its low visitor numbers are both a blessing and a challenge. On the one hand, they have preserved the calm and natural state of the place; on the other, they mean that the conservation of this wetland depends on very limited resources and on the awareness of both local communities and the few visitors. Respecting the surroundings — not polluting the water, not disturbing the birds, not leaving litter, following the guides — is essential for this rare freshwater ecosystem to survive.
Combined with the turtles of Itsamia and the Marine Park on the south coast, Lake Boundouni completes the picture of Mohéli as the most natural island in the Comoros: a place where, within a few kilometres, you go from reefs and whales to a volcanic crater full of herons in the middle of the forest. For anyone looking for authentic, undeveloped, almost untouched nature, this hidden lake is one of the archipelago's quiet gems, and an invitation to discover the heartland of these Indian Ocean islands too.
