Soil erosion and subsequent heavy sedimentation of rivers is very obvious now in many parts of Borneo. This can be a noticeable problem where logging activities take place, and where forest is converted for alternative land use, such as industrial plantations.
Such incidents have come at a cost. There is evidence that some populations of freshwater fish have declined over the last few decades in many Borneo rivers, such as in the Barito. Lakes which are bearing the brunt of logging and conversion of forests and new settlements.
However, new species of freshwater fish continue to be discovered.
The major waterways of Borneo
Borneo’s major rivers are a vivid example of how dynamic the island’s ecosystems can be.
Some of the major waterways that stand out in the Borneo landscape include the Kapuas river (in Kalimantan, Indonesian Borneo), which is 1,143 km,only slightly shorter than the Rhine. The Kapuas flows to the west coast, draining some 2/3 of West Kalimantan province - a watershed of 100,000 km2 (an area slightly larger than Hungary).
Other major rivers in Kalimantan include the Barito (900 km), which flows south, and the Mahakam (775 km), which empties into the Makassar Strait to the east of Borneo.
In Borneo’s inland basins and in the lowlands, several major rivers form extensive lake systems. The Mahakam, Barito, Kapuas and Baram rivers form oxbow
and seasonal lakes in their lowland reaches, some of which are of economic importance for fisheries.
The journeys of Borneo’s rivers
Like sponges, Borneo’s tropical rainforests regulate the quantity of water that drains into streams in the uplands. These merge with others to form larger waterways, which change water volume depending on the seasons. During the rainy season, water levels can change very fast. For example, much of the Kapuas can rise 10-12 metres overnight during heavy rainfall.