The lower reaches of the Kahayan river used to flow through a huge area of peat swamp forest, an unusual ecosystem that is home to many unique or rare species such as orangutans, as well as to slow-growing but valuable trees. The peat swamp forest is a dual ecosystem, with diverse tropical trees standing on a 10m - 12m deep layer of partly decayed and waterlogged plant material, which in turn covers relatively infertile soil. The peat swamp forests were being slowly cleared for small scale farming and plantations before 1997, but most of the original cover remained.