The Kapuas River (or Kapoeas River) is a river in the

Indonesia Indonesia, officially the Republic of Indonesia, is a country in Southeast Asia and Oceania between the Indian and Pacific oceans. It consists of over 17,000 islands, including Sumatra, Java, Sulawesi, and parts of Borneo and New Gui ...

n part of

Borneo Borneo (; id, Kalimantan) is the third-largest island in the world and the largest in Asia. At the geographic centre of Maritime Southeast Asia, in relation to major Indonesian islands, it is located north of Java, west of Sulawesi, and e ...

island, at the geographic center of

Maritime Southeast Asia Maritime Southeast Asia comprises the countries of Brunei, Indonesia, Malaysia, the Philippines, Singapore, and East Timor. Maritime Southeast Asia is sometimes also referred to as Island Southeast Asia, Insular Southeast Asia or Oceanic Sout ...

. At in length, it is the longest river in the island of Borneo and the longest river of IndonesiaMacKinnon, p. 133 and one of the world's longest island rivers. It originates in the

Müller mountain range Müller may refer to: * ''Die schöne Müllerin'' (1823) (sometimes referred to as ''Müllerlieder''; ''Müllerin'' is a female miller) is a song cycle with words by Wilhelm Müller and music by Franz Schubert * Doctor Müller, fictional character ...

at the center of the island and flows west into the

South China Sea The South China Sea is a marginal sea of the Western Pacific Ocean. It is bounded in the north by the shores of South China (hence the name), in the west by the Indochinese Peninsula, in the east by the islands of Taiwan and northwestern Ph ...

creating an extended marshy delta. The delta is located west-southwest of

Pontianak Pontianak or Khuntien is the capital of the Indonesian province of West Kalimantan, founded first as a trading port on the island of Borneo, occupying an area of 118.31 km2 in the delta of the Kapuas River at a point where it is joined ...

, the capital of the

West Kalimantan West Kalimantan ( id, Kalimantan Barat) is a province of Indonesia. It is one of five Indonesian provinces comprising Kalimantan, the Indonesian part of the island of Borneo. Its capital city is Pontianak. The province has an area of 147,307&nbs ...

province.Kapuas River
Encyclopædia Britannica on-line 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 The Barito River is the second longest river in Borneo after the Kapuas River with a total length of and with a drainage basin of in South Kalimantan, Indonesia. It originates in the Muller Mountain Range, from where it flows southward in ...

and discharging into the

Java Sea The Java Sea ( id, Laut Jawa, jv, Segara Jawa) is an extensive shallow sea on the Sunda Shelf, between the Indonesian islands of Borneo to the north, Java to the south, Sumatra to the west, and Sulawesi to the east. Karimata Strait to its no ...

Geography and hydrology

The river is long and up to wide at its delta; with a total area of , the

river basin A drainage basin is an area of land where all flowing surface water converges to a single point, such as a river mouth, or flows into another body of water, such as a lake or ocean. A basin is separated from adjacent basins by a perimeter, ...

covers more than 67% of West Kalimantan.MacKinnon, p. 133 The average annual rainfall in the catchment area is 3,666 mm. The average runoff is around 2,339 mm. The discharge rate varies through the year, averaging around at the delta and upstream, at the confluence of the

Tawang River Tawang is a town and administrative headquarter of Tawang district in the Indian state of Arunachal Pradesh. The town was once the capital of the Tawang Tract, which is now divided into the Tawang district and the West Kameng district. Tawan ...

. 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.MacKinnon, p. 160 The river originates near the center of Borneo, south from the Indonesian-

Malaysia Malaysia ( ; ) is a country in Southeast Asia. The federal constitutional monarchy consists of thirteen states and three federal territories, separated by the South China Sea into two regions: Peninsular Malaysia and Borneo's East Mal ...

n border, in the joint between the western slope of the

Müller Mountain Range Müller may refer to: * ''Die schöne Müllerin'' (1823) (sometimes referred to as ''Müllerlieder''; ''Müllerin'' is a female miller) is a song cycle with words by Wilhelm Müller and music by Franz Schubert * Doctor Müller, fictional character ...

, which runs through the island center, and the southern slope of the Upper Kapuas Range ( id, Kapuas Hulu), which is located more to the west. For about it flows through a mountainous terrain and then descends to a marshy plain. There, the elevation decreases by only over from Putussibau to the river delta.MacKinnon, p. 131 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).MacKinnon, pp. 152, 159 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 river discharges into the

creating a marshy delta, which spreads both inland and into the sea, with the

silt Silt is granular material of a size between sand and clay and composed mostly of broken grains of quartz. Silt may occur as a soil (often mixed with sand or clay) or as sediment mixed in suspension with water. Silt usually has a floury feel ...

deposits extending up to from the Borneo coast. The delta is located west-southwest of

, the capital of

province, which lies at the

equator The equator is a circle of latitude, about in circumference, that divides Earth into the Northern and Southern hemispheres. It is an imaginary line located at 0 degrees latitude, halfway between the North and South poles. The term can also ...

. The delta has five arms, of which the northernmost one is the widest, and is therefore called the Big Kapuas ( id, Kapuas Besar). The largest tributary is the Melawi River, which occurs to the left near the city of Sintang, about 465 km from the mouth. Other major tributaries are the Landak, Kubu, Punggur and Sekayam rivers.South Kalimantan
/ref>

Climate

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. The temperature is rather stable with a typical minimum of and maximum of through the whole year.

Flora and fauna

In the upper and middle reaches, the river flows through dense

tropical forests Tropical forests (a.k.a. jungle) are forested landscapes in tropical regions: ''i.e.'' land areas approximately bounded by the tropic of Cancer and Capricorn, but possibly affected by other factors such as prevailing winds. Some tropical for ...

; the rich flora and fauna are the subject of international research. Discoveries of new species are frequent, such as of the Kapuas mud snake (''Enhydris gyii''), which was discovered in 2003–2005 by German and American

herpetologists Herpetology (from Greek ἑρπετόν ''herpetón'', meaning " reptile" or "creeping animal") is the branch of zoology concerned with the study of amphibians (including frogs, toads, salamanders, newts, and caecilians (gymnophiona)) an ...

. This species is remarkable in that it can spontaneously change its skin color, similar to the

chameleon Chameleons or chamaeleons (family Chamaeleonidae) are a distinctive and highly specialized clade of Old World lizards with 202 species described as of June 2015. The members of this family are best known for their distinct range of colors, bein ...

. Otters and crocodiles are common in the Kapuas River, but frogs are nearly absent.MacKinnon, p. 162

Agile gibbon The agile gibbon (''Hylobates agilis''), also known as the black-handed gibbon, is an Old World primate in the gibbon family. It is found in Indonesia on the island of Sumatra, Malaysia, and southern Thailand. The species is listed as endangere ...

s (''Hylobates agilis''), Müller's Bornean gibbons (''Hylobates muelleri''), Prevost's squirrels (''Callosciurus prevostii'') and

treeshrew The treeshrews (or tree shrews or banxrings) are small mammals native to the tropical forests of South and Southeast Asia. They make up the entire order Scandentia, which split into two families: the Tupaiidae (19 species, "ordinary" treeshre ...

s inhabit the trees above the river.MacKinnon, pp. 52–53 There are two

national park A national park is a natural park in use for conservation purposes, created and protected by national governments. Often it is a reserve of natural, semi-natural, or developed land that a sovereign state declares or owns. Although individual ...

s on the river banks, Betung Kerihun with an area of 8,000 km² and Danau Sentarum (area 1,320 km²), the latter includes the Kapuas Lakes.

Fish

About 300 species of fish have been identified in the river basin, of which 234 are of high economical value. This is more fish species than any other river basin in Indonesia. They belong to 120 genera and 40 families with the two major groups being

cyprinid Cyprinidae is a family of freshwater fish commonly called the carp or minnow family. It includes the carps, the true minnows, and relatives like the barbs and barbels. Cyprinidae is the largest and most diverse fish family and the largest ...

s and

catfish Catfish (or catfishes; order Siluriformes or Nematognathi) are a diverse group of ray-finned fish. Named for their prominent barbels, which resemble a cat's whiskers, catfish range in size and behavior from the three largest species alive, ...

. 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 ''Leptobarbus'' is a genus of cyprinid fish that are native to freshwater habitats in Southeast Asia. They are important food fish. It is the only genus in the subfamily Leptobarbinae. Leptobarbus hoevenii or "sultan fish" migrate the fresh water ...

'', ''

Puntioplites ''Puntioplites'' is a genus of cyprinid fish that occurs in Southeast Asia Southeast Asia, also spelled South East Asia and South-East Asia, and also known as Southeastern Asia, South-eastern Asia or SEA, is the geographical United Nations ...

'', '' Tor'' and others), and species from the

aquarium An aquarium (plural: ''aquariums'' or ''aquaria'') is a vivarium of any size having at least one transparent side in which aquatic plants or animals are kept and displayed. Fishkeepers use aquaria to keep fish, invertebrates, amphibians, aq ...

trade such as the super red arowana and rasboras. Because of

overfishing Overfishing is the removal of a species of fish (i.e. fishing) from a body of water at a rate greater than that the species can replenish its population naturally (i.e. the overexploitation of the fishery's existing fish stock), resulting in t ...

and habitat degradation, several species are threatened. Among these are the

endangered An endangered species is a species that is very likely to become extinct in the near future, either worldwide or in a particular political jurisdiction. Endangered species may be at risk due to factors such as habitat loss, poaching and in ...

arowana and white-edge freshwater whipray, and the wallago catfish, which formerly migrated in large groups in the Kapuas River. Part of the high species diversity in the Kapuas is related to the many different habitats in the river basin. In the headwaters are fast-flowing highland streams, typically dominated by small loaches, and small —often acidic ( blackwater)— forest streams and peat swamps with species such as the tiny ''

Sundadanio ''Sundadanio'' is a genus of cyprinid fishes from freshwater habitats, typically peat swamps and blackwater streams, in Borneo and Sumatra (as well as nearby smaller islands) in southeast Asia. At up to in standard length they are very small, b ...

'' rasboras and macropodusine gouramis. The main river itself also includes several habitats, ranging from the nearshore to open waters. In the deepest sections, no light exists and in one species, '' Lepidocephalus spectrum'', this has resulted in a complete reduction of both eyes and pigmentation (similar to

cavefish Cavefish or cave fish is a generic term for fresh and brackish water fish adapted to life in caves and other underground habitats. Related terms are subterranean fish, troglomorphic fish, troglobitic fish, stygobitic fish, phreatic fish and ...

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 South Sumatra ( id, Sumatra Selatan) is a province of Indonesia. It is located on the southeast of the island of Sumatra, The province spans and had a population of 8,467,432 at the 2020 Census. The capital of the province is Palembang. The prov ...

Java Java (; id, Jawa, ; jv, ꦗꦮ; su, ) is one of the Greater Sunda Islands in Indonesia. It is bordered by the Indian Ocean to the south and the Java Sea to the north. With a population of 151.6 million people, Java is the world's mo ...

and

Malay Peninsula The Malay Peninsula ( Malay: ''Semenanjung Tanah Melayu'') is a peninsula in Mainland Southeast Asia. The landmass runs approximately north–south, and at its terminus, it is the southernmost point of the Asian continental mainland. The ar ...

. Apart from fish, there are numerous crabs, prawns,

water strider The Gerridae are a family of insects in the order Hemiptera, commonly known as water striders, water skeeters, water scooters, water bugs, pond skaters, water skippers, or water skimmers. Consistent with the classification of the Gerridae as tr ...

s and other aquatic insects.MacKinnon, p. 132 The rich flora and fauna results in very complex

food chain A food chain is a linear network of links in a food web starting from producer organisms (such as grass or algae which produce their own food via photosynthesis) and ending at an apex predator species (like grizzly bears or killer whales), de ...

s, 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 which bend over its waters.MacKinnon, p. 161 The feeding habits of the fish in the Kapuas River are distributed as follows: 54% are

omnivore An omnivore () is an animal that has the ability to eat and survive on both plant and animal matter. Obtaining energy and nutrients from plant and animal matter, omnivores digest carbohydrates, protein, fat, and fiber, and metabolize the nu ...

s; 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 Algae (; singular alga ) is an informal term for a large and diverse group of photosynthetic eukaryotic organisms. It is a polyphyletic grouping that includes species from multiple distinct clades. Included organisms range from unicellular micr ...

Transport and economic value

The Kapuas River is the major waterway connecting the center of the island with its western coast. The large river width and depth (up to 27 meters) support intensive cargo and passenger shipping over most of the river length. Ships with a

draft Draft, The Draft, or Draught may refer to: Watercraft dimensions * Draft (hull), the distance from waterline to keel of a vessel * Draft (sail), degree of curvature in a sail * Air draft, distance from waterline to the highest point on a vesse ...

of up to 3 meters can navigate up to Sintang, 465 km from the mouth, and those with a draft up to 2 meters can reach the town of

Putussibau Putussibau is an Indonesian town in Kapuas Hulu Regency, West Kalimantan. It sits on the river Kapuas, with the main part of the town located on the right banks, or north, of the river. Officially an administrative village (''Kelurahan Putussibau ...

(902 km from the mouth). Logging and rafting of timber occur all along the river. Fishing is also common, especially at the Kapuas Lakes and near the river delta.MacKinnon, p. 457 The Tayan Bridge, 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 existing bridge.

References

Bibliography

*MacKinnon, Kath
The ecology of Kalimantan
Oxford University Press, 1996, {{Coord, 0.2660, S, 109.8754, E, region:ID_type:river, display=title Rivers of West Kalimantan Landforms of West Kalimantan Rivers of Indonesia