The Kapuas River is a river in the Indonesia

Indonesia

Indonesia , officially the Republic of Indonesia , is a country in Southeast Asia and Oceania. Indonesia is an archipelago comprising approximately 13,000 islands. It has 33 provinces with over 238 million people, and is the world's fourth most populous country. Indonesia is a republic, with an...

n part of Borneo

Borneo

Borneo is the third largest island in the world and is located north of Java Island, Indonesia, at the geographic centre of Maritime Southeast Asia....

 island, at the geographic center of Maritime Southeast Asia

Maritime Southeast Asia

Maritime Southeast Asia refers to the maritime region of Southeast Asia as opposed to mainland Southeast Asia and includes the modern countries of Indonesia, Malaysia, the Philippines, Brunei, East Timor and Singapore....

. At 1143 kilometres (710.2 mi) in length, it is the longest river of Indonesia and one of the world's longest island rivers. It originates in the Müller mountain range at the center of the island and flows west into the South China Sea

South China Sea

The South China Sea is a marginal sea that is part of the Pacific Ocean, encompassing an area from the Singapore and Malacca Straits to the Strait of Taiwan of around...

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

Pontianak, Indonesia

Pontianak is the capital of the Indonesian province of West Kalimantan. It is a medium-size industrial city on the island of Borneo. Pontianak occupies an area of 107.82 km² in the delta of the Kapuas River...

, the capital of West Kalimantan

West Kalimantan

West Kalimantan is a province of Indonesia. It is one of four Indonesian provinces in Kalimantan, the Indonesian part of the island of Borneo. Its capital city Pontianak is located right on the Equator....

 province. This Kapuas River should be distinguished from another Kapuas River

Kapuas River (Barito River)

The Kapuas River is a river in the Indonesian part of Borneo island. It originates in the Müller Mountain Range at the center of the island and flows south until merging with the Barito River and discharging into the Java Sea...

, which starts on the other side of the same mountain range in central Borneo, but flows to the south, merging with the Barito River

Barito River

Barito is a 890 km long river, located in South Kalimantan, Indonesia. It originates in the Muller Mountain Range from where it flows southward into the Java Sea...

 and discharging in to the Java Sea

Java Sea

The Java Sea is a large shallow sea on the Sunda Shelf. It was formed as sea levels rose at the end of the last ice age. The Java Sea lies between the Indonesian islands of Borneo to the north, Java to the south; Sumatra to the west, and Sulawesi to the east...

.

Geography and hydrology

The river is 1143 km (710.2 mi) long and up to 700 m (2,296.6 ft) wide at its delta; with a total area of 98,749 km², the river basin covers more than 67% of West Kalimantan. The discharge rate varies through the year, averaging around 6,000–7,000 m³/s at the delta and 2,000 m³/s upstream, at the confluence of the Tawang River. The discharge peaks during the rainy seasons in April and November, during which the water level may rise by 10–12 m overnight, overflowing river banks and flooding the nearby areas.

The river originates near the center of Borneo, south from the Indonesian-Malaysian border, in the joint of 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 165 km it flows through a mountainous terrain and then descends to a marshy plain. There, the elevation decreases by only 50 metres (164 ft) over 900 km (559.2 mi) from Putussibau to the river delta. About 350 km 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 300 mm, the river overflows its banks, diverting much of its waters to the lakes at a rate of up to 1,000 m³/s, and forming a single water mass 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 South China Sea

South China Sea

The South China Sea is a marginal sea that is part of the Pacific Ocean, encompassing an area from the Singapore and Malacca Straits to the Strait of Taiwan of around...

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

Silt

Silt is granular material of a size somewhere between sand and clay whose mineral origin is quartz and feldspar. Silt may occur as a soil or as suspended sediment in a surface water body...

 deposits extending up to 50–60 km from the island. The delta is located west-southwest of Pontianak

Pontianak, Indonesia

Pontianak is the capital of the Indonesian province of West Kalimantan. It is a medium-size industrial city on the island of Borneo. Pontianak occupies an area of 107.82 km² in the delta of the Kapuas River...

, the capital of West Kalimantan

West Kalimantan

West Kalimantan is a province of Indonesia. It is one of four Indonesian provinces in Kalimantan, the Indonesian part of the island of Borneo. Its capital city Pontianak is located right on the Equator....

 province which lies at the equator

Equator

An equator is the intersection of a sphere's surface with the plane perpendicular to the sphere's axis of rotation and containing the sphere's center of mass....

. The delta has five arms, of which the northernmost one is the widest, and is therefore called the Big Kapuas . The largest tributary is the Melawi River

Melawi River

Melawi River is a river of northwestern Borneo, Indonesia.It is a tributary of the Kapuas River. The people in upper reaches of the Melawi speak Ot Danum and elsewhere along the river speak variants of the Malay language and the river banks are inhabited by the Malay and Dayak ethnic groups.A major...

, 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

Sekayam River

Sekayam River is a river of Borneo, Indonesia.It is a tributary of the Kapuas River. The Program Pemberdayaan Sistem Hutan Kerakyatan has a scheme on the river aimed at reducing the level of mercury content absorbed by humans....

 rivers.

Climate

The climate is warm and very humid, with the average annual precipitation ranging from year to year between 2,863 and 5,517 mm, 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 24 °C (75.2 °F) and maximum of 32 °C (89.6 °F) through the whole year.

Flora and fauna

In the upper and middle reaches, the river flows through dense tropical forests; the forests are rich in flora and fauna and are the subject of international research. Discoveries of new species are frequent, such as of the Kapuas mud snake

Kapuas mud snake

The Kapuas mud snake is a native Borneo species of snakes that can change its epidermal color spontaneously. Named after the Kapuas River, the snake's chameleon-like behaviour was discovered in 2005 accidentally when a specimen was put in a dark bucket. The snake's skin turned pale white 20...

 (Enhydris gyii), which was discovered in 2003–2005 by the German and American herpetologists

Herpetology

Herpetology is the branch of zoology concerned with the study of amphibians and reptiles...

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

Chameleon

Chameleons are a distinctive and highly specialized clade of lizards. They are distinguished by their parrot-like zygodactylous feet, their separately mobile and stereoscopic eyes, their very long, highly modified, and rapidly extrudable tongues, their swaying gait, the possession by many of a...

.

About 300 species of fish have been identified in the river, of which 234 are of high economical value. They belong to 120 genera and 40 families with the two major groups being carp

Carp

Carp are various species of oily freshwater fish of the family Cyprinidae, a very large group of fish native to Europe and Asia. The cypriniformes are traditionally grouped with the Characiformes, Siluriformes and Gymnotiformes to create the superorder Ostariophysi, since these groups have certain...

 and catfish

Catfish

Catfishes 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 heaviest and longest, the Mekong giant catfish from Southeast Asia and the second longest, the wels catfish of Eurasia, to detritivores...

. More than 30% of the species originate from the sea and inhabit the delta areas. Owing to the warm climate and abundance of food, most fishes breed all through the year with only a few species like fire eel

Fire eel

The fire eel is a large freshwater fish found in Cambodia, Indonesia, Laos, Malaysia, Thailand, and Vietnam.-Description:...

 (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 was connected to the rivers of South Sumatra

South Sumatra

South Sumatra is a province of Indonesia.-Geography:It is on the island of Sumatra, and borders the provinces of Lampung to the south, Bengkulu to the west, and Jambi to the north...

, Java

Java

Java is an island of Indonesia. With a population of 135 million , it is the world's most populous island, and one of the most densely populated regions in the world. It is home to 60% of Indonesia's population. The Indonesian capital city, Jakarta, is in west Java...

 and Malay Peninsula

Malay Peninsula

The Malay Peninsula or Thai-Malay Peninsula is a peninsula in Southeast Asia. The land mass runs approximately north-south and, at its terminus, is the southern-most point of the Asian mainland...

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

Water strider

Gerridae is a family of true bugs in the order Hemiptera, commonly known as water striders, water bugs, magic bugs, pond skaters, skaters, skimmers, water scooters, water skaters, water skeeters, water skimmers, water skippers, water spiders, or Jesus bugs...

s and other aquatic insects. The rich flora and fauna results in very complex food chain

Food chain

A food web depicts feeding connections in an ecological community. Ecologists can broadly lump all life forms into one of two categories called trophic levels: 1) the autotrophs, and 2) the heterotrophs...

s, with fishes consuming foods ranging from fruits to other fish. For example, Hemirhamphodon

Hemirhamphodon

Hemirhamphodon is a genus of halfbeak found in peaty and lowland forest streams in Southeast Asia. Six species are known, all relatively small, the largest species being about 10 cm in length...

 pogonognathus feeds exclusively on terrestrial insects. The abundant fruits and seeds enter the river after falling from large trees which bend over its waters. The feeding habits of the fish in the Kapuas River are distributed as follows: 54% are omnivore

Omnivore

Omnivores are species that eat both plants and animals as their primary food source...

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

Algae are a large and diverse group of simple, typically autotrophic organisms, ranging from unicellular to multicellular forms, such as the giant kelps that grow to 65 meters in length. They are photosynthetic like plants, and "simple" because their tissues are not organized into the many...

.
Otters and crocodiles are common in the Kapuas River, but frogs are nearly absent. Agile Gibbon

Agile Gibbon

The agile gibbon , also known as the black-handed gibbon, is an Old World primate in the Hylobatidae or gibbon family, a group also collectively referred to as the "lesser apes"...

 (Hylobates agilis), Müller's Bornean Gibbon

Müller's Bornean Gibbon

Müller's Bornean gibbon , also known as the grey gibbon, is a primate in the Hylobatidae or gibbon family.Unlike other gibbon species, Müller's Bornean gibbon does not show sexual dimorphism in its fur coloration. Its fur is grey or brown colored with a ring of bright fur around its face. On the...

 (Hylobates muelleri), Prevost's Squirrel (Callosciurus prevostii) and treeshrew

Treeshrew

The treeshrews are small mammals native to the tropical forests of Southeast Asia. They make up the families Tupaiidae, the treeshrews, and Ptilocercidae, the pen-tailed treeshrews, and the entire order Scandentia. There are 20 species in 5 genera...

s inhabit the trees above the river.

There are two national park

National park

A national park is a reserve of natural, semi-natural, or developed land that a sovereign state declares or owns. Although individual nations designate their own national parks differently A national park is a reserve of natural, semi-natural, or developed land that a sovereign state declares or...

s on the river banks, Betung Kerihun

Betung Kerihun National Park

Betung Kerihun National Park is a national park in the province of West Kalimantan on the island of Borneo, Indonesia. It is located inland, along the Malaysian border...

 with an area of 8,000 km² and Danau Sentarum

Danau Sentarum National Park

The Danau Sentarum National Park is a national park protecting one of the world's most biodiverse lake systems, located in Borneo Island, West Kalimantan Province, Indonesia. It lies in the upper Kapuas River basin some 700 kilometres upstream from the delta. The basin is a vast floodplain,...

 (area 1,320 km²), the latter includes the Kapuas Lakes.

Transport and economic value

The Kapuas River is the major waterway connecting the central 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 (hull)

The draft of a ship's hull is the vertical distance between the waterline and the bottom of the hull , with the thickness of the hull included; in the case of not being included the draft outline would be obtained...

 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 city of 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.