Kapuas River

The Kapuas River is a massive waterway in Indonesia. It is located on the island of Borneo. This river is the longest on the island of Borneo. It is also one of the longest island rivers in the world. The river flows through the West Kalimantan province. It sits near the geographic center of Maritime Southeast Asia.

The river follows a specific path from the center of the island to the sea. It originates in the Müller mountain range. It also sits at the joint of the Upper Kapuas Range. The river flows through mountainous terrain first. Then it descends into a marshy plain. The elevation drops very little between Putussibau and the delta. Finally, the river discharges into the South China Sea. This creates an extended, marshy delta. The delta has five arms. The widest arm is called the Big Kapuas.

A unique system of lakes sits near the northern shore of the river. These are the Kapuas Lakes. They are connected to the river by many channels. There are many different lakes in this system. These include Bekuan, Belida, and Genali. Other lakes are Keleka Tangai, Luar, and Pengembung. Smaller lakes include Sambor, Sekawi, Sentarum, Sependan, Seriang, Sumbai, Sumpa, and Tekenang. When monthly precipitation exceeds 300 mm, the river overflows. It diverts water to the lakes at rates up to 1,500 m3/s. This process prevents massive flooding in the lower reaches. It also helps fish migrate to the lakes for spawning.

The climate around the river is warm and very humid. The average annual rainfall in the catchment area is 3,666 mm. Annual precipitation can range between 2,863 and 5,517 mm. This creates a very wet environment. The number of rainy days varies between 120 and 309 per year. Temperatures remain stable throughout the year. The river has many different habitats. Some areas have fast-flowing highland streams. Other areas have acidic blackwater forest streams. There are also peat swamps. The river's discharge varies throughout the year. It peaks during the rainy seasons in April and November. During these times, water levels can rise by 1 meter overnight.

The river is home to incredible biodiversity. Scientists frequently discover new species in the dense tropical forests. For example, herpetologists found the Kapuas mud snake between 2003 and 2005. This snake can change its skin color like a chameleon. Many animals live in the trees above the water. These include agile gibbons and Müller's Bornean gibbons. You can also find otters and crocodiles in the river. There are about 300 fish species in the river basin. This is more fish species than any other river basin in Indonesia. One famous fish is the super red arowana.

Fish in the Kapuas have many different roles in the food chain. About 54% of the fish are omnivores. About 36% are carnivores. The remaining 10% are herbivores. Some fish eat only insects, like the Hemirhamphodon pogonognathus.

In the deepest sections, there is no light. One species, Lepidocephalus spectrum, has lost its eyes and pigmentation. This is similar to how cavefish live. Many fish species are economically important for food. These include Pangasius catfish and giant gourami. However, some species like the arowana are now threatened. This is due to habitat degradation and overfishing.

The Kapuas River is vital for transport and the economy. It connects the center of Borneo to the western coast. The river is very deep, reaching up to 27 meters. This allows large ships to carry cargo and passengers. Ships with a 3-meter draft can reach Sintang. Ships with a 2-meter draft can reach Putussibau. This is 902 km from the mouth. People use the river for fishing and logging timber.

Large bridges also cross the water. The Tayan Bridge is the longest bridge in Kalimantan. The river remains a central part of life in West Kalimantan.