Река Капуас: Самая длинная река Калимантана и Индонезии

River in West Kalimantan, Indonesia
the river in western Borneo

The Kapuas River (or Kapoeas River) is a river in the Indonesian part of Borneo island, at the geographic center of Maritime Southeast Asia. At in length, it is the longest river in the island of Borneo and the longest river in Indonesia and one of the world's longest island rivers. This Kapuas River should be distinguished from another Kapuas River, which starts on the other side of the same mountain range in central Borneo but flows to the south, merging with the Barito River and discharging into the Java Sea.

The river is long and up to wide at its delta; ~ the river basin covers more than 67% of West Kalimantan. The discharge rate varies through the year, averaging around at the delta and upstream, at the confluence of the Tawang. The discharge peaks during the rainy seasons in April and November, during which the water level may rise by overnight, overflowing river banks and flooding the nearby areas. The river originates near the center of Borneo, south of the Indonesian Malaysian border, in the joint between the western slope of the Müller Mountain Range, which runs through the island center, and the southern slope of the Upper Kapuas Range , which is located more to the west. For about it flows through a mountainous terrain and then descends to a marshy plain. About from the source, near the northern shore of the river, lies a system of Kapuas Lakes which are connected to the river by numerous channels. These lakes are Bekuan (area 1,268 hectares), Belida (600 ha), Genali (2,000 ha), Keleka Tangai (756 ha), Luar (5,208 ha), Pengembung (1,548 ha), Sambor (673 ha), Sekawi (672 ha), Sentarum (2,324 ha), Sependan (604 ha), Seriang (1,412) Sumbai (800 ha), Sumpa (664) and Tekenang (1,564 ha). When the monthly precipitation exceeds about , the river overflows its banks, diverting much of its waters to the lakes at a rate of up to , and forming a single volume of water with them. This outflow prevents massive flooding of the lower reaches of the river; it also promotes fish migration from the river to the lakes for spawning, but drives birds away from the lakes.

The climate is warm and very humid, with the average annual precipitation ranging from year to year between , and the number of rainy days between 120 and 309; the largest precipitation was observed in 1976 (120 rainy days) and the wettest in 1988, with only 184 rainy days.

In the upper and middle reaches, the river flows through dense tropical forests; the rich flora and fauna are the subject of international research. Otters and crocodiles are common in the Kapuas River, but frogs are nearly absent. Agile gibbons (Hylobates agilis), Müller's Bornean gibbons (Hylobates muelleri), Prevost's squirrels (Callosciurus prevostii), and treeshrews inhabit the trees above the river. There are two national parks on the river banks, Betung Kerihun with an area of 8,000 km2, and Danau Sentarum (an area of 1,320 km2), the latter includes the Kapuas Lakes. They belong to 120 genera and 40 families with the two major groups being cyprinids and catfish. More than 30% of the species originate from the sea and inhabit the delta areas. Among the economically important species are food fish such as Pangasius catfish, giant gourami, kissing gourami, snakeheads, and large barbs (Leptobarbus, Puntioplites, Tor, and others), and species from the aquarium trade such as the super red arowana and rasboras. Owing to the warm climate and abundance of food, most fishes breed all through the year with only a few species like fire eel (Mastacembelus erythrotaenia) having certain reproduction periods. The number of individuals per species is relatively low. The large variety of species may be explained by the fact that some 6,000 years ago, the Kapuas River, as a tributary of the Sunda River, was connected to other tributary rivers of South Sumatra, Java, and the Malay Peninsula. Apart from fish, there are numerous crabs, prawns, water striders, and other aquatic insects. The rich flora and fauna result in very complex food chains, with fishes consuming foods ranging from fruits to other fish. For example, Hemirhamphodon pogonognathus feeds exclusively on terrestrial insects. Abundant fruits and seeds enter the river after falling from large trees that bend over its waters. The feeding habits of the fish in the Kapuas River are distributed as follows: 54% are omnivores; 36% are carnivorous and eat other fish (14%), insects (5%), and mixed small forest animals (17%). The remaining 10% are herbivorous, with 4% of them specialising in algae. The Tayan Bridge which opened in 2016, crosses over the river and is the longest bridge in Kalimantan. Another major bridge over the area is the Kapuas I Bridge. In 2022, the local government decided to build a newer bridge to accommodate increased traffic in commuters and goods, located to be in parallel with the existing bridge.