Lake Matano (Indonesian: Danau Matano), also known as Matana, is a natural lake in South Sulawesi, Indonesia. Lake Matano is home to many species of endemic fish and other animals (e.g. Caridina shrimps, Parathelphusid crabs and Tylomelania snails as well as many plants. The endemic fishes of Matano have been compared to the species swarms of the Rift Valley Lakes of Africa. While not as diverse, they are thought to have all arisen from a single ancestor species and diversified into numerous different species, which now fill many of the previously vacant ecological niches, as can be seen in the family Telmatherinidae. Endemic and near-endemic fishes from other families include Glossogobius matanensis, Mugilogobius adeia, Nomorhamphus weberi and Oryzias matanensis. Many of the endemics are seriously threatened due to pollution and predation/competition from a wide range of introduced fishes, including flowerhorn cichlids. The water snake Enhydris matannensis is only known from the vicinity of Lake Matano and on Muna Island.
Although large areas are cleared for mining the company has a well regarded rehabilitation program and award-winning sediment control systems. The vast areas of rainforest are replaced by mono-cultures of largely non-native trees to counter erosion but doing little to address the loss of biodiversity and the environmental services this provides. The waters of Lake Matano are exceptionally clear, visibility is good, and many of the fish species are highly dependent on visual cues and colour perception for their mating behaviour. If the sediment washing into the lake continues to increase, the likelihood is that many of these endemic species will be lost.