The lower Kayahan flows through a rich and unusual environment of peat swamp forests, which has been severely degraded by an unsuccessful program to convert a large part of the area into rice paddies, compounded by legal and illegal forestry.

The Ot Danum remains in the upstream regions of the Kahayan, Barito, Kapuas, and Rungan rivers and preserves a traditional way of life.

Village elders practice traditional medicine and mark their status with intricate body tattoos and heavy ear adornments.

[10] The Ngaju have moved downstream, and to some extent assimilated with the mixed population of the towns further down the river, which includes Javanese, Maduranese, Batak, Toraja, Ambonese, Bugis, Palembang, Minang, Banjarese, Makassar, Papuan, Balinese, Acehnese, and Chinese.

[11] 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.

[14] Following test drilling, a consortium of Canadian and Indonesian companies announced in 1997 that in-situ gold resources were at least 3.4 million ounces.

[16] A large number of informal prospectors are undertaking alluvial operations within the river system, and mining hard rock gold veins.

Vulnerable bird species include the large green pigeon (Treron capellei) and possibly Storm's stork (Ciconia stormi) and lesser adjutant (Leptoptilus javanicus).

The more badly damaged eastern part, between the Sabangau and the Kayahan, is still officially designated for agriculture, although no further efforts are being made to make it suitable for this purpose.