Lac Dziani

Lac Dziani (officially Dziani Dzaha, "sacred lake" in Shimaore) is a volcanic crater 350 metres in diameter filled with unique emerald-green water, located in northern Petite-Terre. Formed about 7,000 years ago by a phreatomagmatic explosion (meeting between magma and the salt water table), it is the most recent volcanic formation of the Mahoran archipelago and one of the most singular landscapes in the entire French Indian Ocean.

The lake is only 4 metres deep and filled with saline and alkaline water (pH 9, salinity higher than the sea). Its intense emerald colour is due to the cyanobacteria that develop in this extreme environment — the same types of bacteria that produced our atmosphere's oxygen 2.5 billion years ago. The lake is considered one of the world's most interesting sites for studying the origins of life and Martian analogues (NASA has conducted studies on its cyanobacteria). Swimming is strictly prohibited: the lake is sacred to the Mahorans (local legends evoke a djinn inhabiting its depths) and the alkaline water would be harmful to skin.

A panoramic trail of 4 kilometres circles the crater on its crest (1h30 walk, low elevation — about 100 metres). The well-marked trail offers exceptional views throughout: over the crater and its emerald water, over the surrounding turquoise lagoon, over Petite-Terre and Pamandzi to the south, and in clear weather as far as Grande-Terre to the west.

The trail's fauna is rich for the keen observer. Brown lemurs (endemic to Mayotte, Eulemur fulvus) are sometimes visible in the trees around the lake, particularly early in the morning. Giant fruit bats (Pteropus seychellensis) come out at dusk in impressive colonies. Several bird species inhabit the trees.

The legend of Lac Dziani is part of Mahoran culture. Elders say that a djinn inhabits the lake's depths and that its anger manifests in surface bubbling. Swimming is prohibited not only for ecological reasons but also out of respect for the sacred character. Several traditional ceremonies (offerings, prayers) take place on the shores.