Mahakam Tengah is the third biggest swamp in Kalimantan (see Danau Sentarum and Sungai Negara). Biologically, the area is the famous area for Orcaella brevirostris. The area covers 400000 ha, with Lake Jampang as the main lake. Melintang Lake and Semayang Lake has acid water and low fauna diversity.The lakes are very important as buffer area to regulate Mahakam River. The environment of the area is very dynamic and unstable.
There is very limited information about birds from this area. The lake is often visited by wetland species such as Whistered Tern Chlidonias hybridus and Little Tern Sterna albifrons and some species of herons. In dry season, muddy area & grassland support very big number of migratory birds. The highest number recorded was Lesser Adjutant Leptoptilus javanicus (170 birds) on August 1996. A thousand Javan Pond-heron are recorded breeding in August (no year), together with other herons, although the exactly site is not yet identified.The biggest colony of waterbirds, probably is Oriental Darter Anhingia melanogaster and Lesser Adjutant Leptoptilus javanicus, reported by local people from Muara Enggelam, the area that have not been visited by ornithologist. This site probably is the most important site for waterbirds colony in Kalimantan. Beside that, this area probably important for Moorhen, around 250-500 Purple Swamphen Porphyrio porphyrio recorded around Danau Jempang on October 1996. Pheasant-tailed Jacana ia a common bird on Rawa Negara, although it is a rare bird in this area. Whistered Tern Chlidonia hybridus lives along the year (the highest number is 3758 bird on 31 August 1997). Around 658 Little Tern Sterna albifrons recorded at the same periode. Breeding colony of Little Tern is founded in 2 locations. Wandering Whistling-duck reported breeding in this area but the exact site is not yet identified. Grey-headed Fish-eagle Ichthyophaga ichthyaetus recorded in small population, and Chestnut-checked Starling Sturnus philippensis recorded up to 5000 birds.In the forest around the lakes, there are Wallace's Hawk-eagle Spizaetus nanus, Long-billed Partridge Rhizothera longirostris, Crested Fireback Lophura ignita, Large Frogmouth Batrachostomus auritus, Gould's Frogmouth Batrachostomus stellatus, Javan Frogmouth Batrachostomus javensis, Sunda Wrinkled Hornbill Aceros corrugatus (recorded up to 75 birds), Garnet Pitta Pitta granatina, Blue-headed Pitta Pitta baudii, Bornean Blue-flycatcher Cyornis superbus, Rufous-chested Flycatcher Ficedula dumetoria and Bornean Bristlehead Pityriasis gymnochepala.
Non-bird biodiversity: Orcaella brevirostris, Nasalis larvatus, Presbytis frontata, Presbytis rubicunda, Hylobathes muelleri, Neofelis brevirostris, Neofelis nebulosa, Helarctos malayanus, Crocodylus porosus, Crocodylus siamensis and Tomistoma sclegelii (Scott 1989, Momberg et.al.1998a,b, Colijn 2000).
BirdLife International (2020) Important Bird Areas factsheet: Lahan Basah Mahakam Tengah. Downloaded from http://www.birdlife.org on 25/02/2020.