Unnamed forest stream in south Sarawak, Borneo

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Malaysia, Borneo, Sarawak

Located in Southeast Asia, Borneo is the third largest island in the world (after Greenland & New Guinea). The island is divided among three countries: Malaysia, Indonesia (Kalimantan), and Brunei.

Borneo is home to some of the most biodiverse and unique ecosystems in the world, including the peat swamp forests – a type of tropical forest typically found in low-lying areas with poor drainage and high levels of rainfall.

Submitted by
Gábor Juhász-Tóth
Approved by
Heok Hee Ng & Greg Martin
Geographical region
Southeastern Asia
Drainage Basin
River catchment
Water body type
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Water body course
Water body: tributary of
Tributary name

Videos above and below water

Water Chemistry

Water information

Water type
Fresh water
Water color
Black water
Water transparency
Concentration of sediments
Water temperature
22-29 °C
Water flow/curent

Chemical parameters

Dissolved Oxygen

Substrate in nature

Stone form
Submerged terrestrial vegetation

Aquatic Biotope

Date of collecting
Collecting area
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Surrounding area

Borneo peat swamp forests are characterized by their nutrient-poor, waterlogged soils, composed of layers of decomposing plant material that have accumulated over thousands of years. The pH of these soils is typically between 3.0 and 5.5, which is significantly more acidic than most other soil types.

The low pH of peat swamp forest soils is due to the accumulation of organic acids produced by the breakdown of plant materials in the anaerobic conditions of the forest floor. These acids create a challenging environment for many plants and animals to survive in.

However, some species have evolved adaptations that allow them to thrive in these acidic conditions, such as specialized root systems and enzymes that can tolerate or even utilize the acidic environment. Peat swamp forests would be considered blackwater ecosystems for their low conductivity and pH.

Changes to the pH of peat swamp forest soils can significantly impact the health and diversity of the ecosystem. For example, drainage and deforestation can lead to increased soil pH, which can alter the composition of plant and animal communities. In addition, changes in pH can affect the availability of nutrients and other essential elements required for the growth and survival of plants and animals.

The Borneo peat swamp forests are home to a diverse range of aquatic life, including many fish species. These forests have unique soil and water chemistry – low in oxygen and high in acidity. The acidic conditions have a significant impact on the plants and animals that live in the forests. Despite these challenging conditions, many fish species have adapted to thrive in this environment, including a variety of wild bettas.

Fish are an important part of the Borneo peat swamp ecosystem, providing food sources for larger predators such as birds, reptiles, and mammals. Some fish species native to these forests include the Asian Arowana and a variety of gouramis (such as the chocolate gourami and the giant red tail gourami), rasboras (such as Rasbora sarawakensis), and catfish (such as the glass catfish and Borneo walking catfish). These species are well-adapted to low-oxygen levels and acidic water.
Other fish species in the peat swamp forests include the Climbing Perch, which are part of the Anabantidae family (along with bettas and gouramis). This hardy freshwater fish can survive in the low-oxygen conditions of the swamp by breathing oxygen from the surface.

The forests of Borneo supply local waterways with a variety of leaf litter. To recreate a peat swamp can be considered jackfruit leaves, guava leaves, jambolan leaves, Melastoma roots, cocoa pods, macaranga leaves, sappan wood pods, sterculia pods.

Underwater landscape

The dense rainforest above the small swamp does not let the light to penetrate the water surface and the substrate is littered with fallen tree branches and rotting leaves. I used sand, and a very soft water <50µS/cm and a lot of driftwood and leaves to obtain a typical stained dark brown water. Humic acids released by those botanical are important to have a natural feel and extremly important for the growth of beneficial microbe colonies as decomposition occurs. Swimming and pattern simulate a dead leaf.

Threats to ecology

Despite their importance for biodiversity and carbon storage, these forests have been heavily impacted by human activities, leading to the loss of many species. Peat swamp forests and their fish populations are under threat from deforestation and drainage for agriculture, logging, and palm oil plantations.

These activities are causing the loss and degradation of forests, leading to habitat destruction and fragmentation. Conservation efforts are needed to protect the Borneo peat swamp forests and many activist groups are working towards sustainable solutions. This includes creating protected areas and sustainable management practices for the ecosystems which include the fish populations within them.

Riparian zone

Trees near the aquatic habitat
Few -


  • Unique Southeast Asian peat swamp forest habitats have relatively few distinctive plant species by W. Giesen, L.S. Wijedasa and S.E. Page
  • Biodiversity research and conservation in Borneo’s peat-swamp forests by Harrison, Susan Cheyne, David A. Ehlers Smith

Comment by the expert

Heok Hee Ng: Habitat description is detailed and threats are correctly identified.

Greg Martin: Thorough.