When you think of Singapore's waterways, you may think of the many canals that cut through housing estates or the wider, scenic rivers such as Kallang River or Singapore River.
But there is a humbler kind of waterway that runs quietly through shady forested areas and which is more than pulling its weight in supporting native wildlife.
These are the natural freshwater streams.
Small, rarely deeper than 1m and slow-flowing, they are often the last of the natural habitats for native species, which struggle to find a place to live in built-up, urbanised Singapore.
These indigenous species include a spider that "walks" on water to prey on small fishes, called Singapore fishing spider (Thalassius albocinctus). Another is a male forest fighting fish which carries eggs in its mouth (Betta pugnax) and a forest-walking catfish that breathes in water and on land (Clarias leiacanthus).
Forest streams were in the news recently when it was announced that two rare streams in Lentor forest will be cleared for redevelopment, together with most of the forest.
Types of streams
There are different types of freshwater habitats here. Most are unaffected by tides and the water is usually fresh as opposed to waterways with partly saline water such as estuaries, where rivers meet the sea.
NATURAL FOREST STREAMS
They are usually small, shallow, slow-flowing and have slightly acidic waters. Most of them are found within nature reserves.
They are deeply shaded by the forest tree canopy and are quite cool. Due to the lack of light, few aquatic plants grow in these streams.
The wildlife within these streams have adapted to these environmental conditions and do not occur in other kinds of streams or in reservoirs, which are more open.
In fact, natural forest streams are the only refuge for most of Singapore's native aquatic wildlife, such as Singapore fishing spider (Thalassius albocinctus) and the forest-walking catfish (Clarias leiacanthus).
They are usually larger than natural forest streams with water of almost neutral pH.
Usually artificial or modified, for instance, straightened, widened or deepened, they are found in rural areas or urban parks and sometimes just outside the nature reserves.
The stream banks are often made of grassy lawns instead of forest trees. Ornamental or wayside shrubs and trees may be planted, but are not enough to form a closed canopy that completely shades the stream. As there is more light, aquatic plants may grow within the streams.
Only a few tough, adaptable native species such as the whitespot can be found in these rural streams, but the majority of the species are introduced or are exotic species that are more adapted to such environmental conditions.
URBAN DRAINS AND CANALS
These are artificial freshwater streams that are found all over Singapore. Their environmental conditions can be relatively harsh and unpredictable because the canals are completely concretised and exposed, with large changes in water level.
This is because they are designed to alleviate floods by carrying away large volumes of water that run off from urban areas during rain.
Only a few of the tougher native species such as the white spot can be found here, but the majority are introduced species, such as pet fish released by their owners.
Source: Dr Darren Yeo
There are "at least dozens" of similar streams in Singapore, most of which are found in the Central Catchment Nature Reserve and Bukit Timah Nature Reserve, says Dr Darren Yeo Chong Jinn, an assistant professor at the department of biological sciences at the National University of Singapore.
He has been doing research on freshwater habitats since the mid-1990s.
Forest streams are different from other freshwater habitats such as concrete drains, canals, ponds and reservoirs because they have a high percentage of Singapore's original biodiversity.
These include at least 30 species of freshwater fish and more than 10 species of freshwater crabs and shrimps.
There are also native freshwater species of spiders, snakes, frogs, turtles and aquatic insects, as well as dragonflies and damselflies, which lay eggs in the water that hatch into aquatic larvae.
Native creatures thrive in and around natural streams because they provide a cool environment well-shaded by the forest canopy and by plants growing along the stream banks.
The stream beds are also made up of sand, clay, or mud and are often full of leaf litter and woody debris, which animals like to use as a cover from their predators.
According to Dr Yeo, the best time to sight the animals is in the morning and evening, when there is generally more activity.
He advises visitors to remain still at a spot and take some time to let their eyes adjust to the stream as its reflecting surface may make it difficult to see things at first.
He says: "This also gives the stream animals time to get acclimatised to the observer and the potentially big shadow cast over them."
He adds that many forest stream fish are small and can be better observed with a pair of small binoculars.
Also watch out for wildlife such as frogs and reptiles at the edges of the stream.
He says: "If you are lucky, you may even catch glimpses of birds perched or flying through the surrounding vegetation and other mammals coming by to take a sip of water."
But remember not to step into the stream, as you may pollute the water or accidentally step on aquatic animals.
On the shy creatures, he says: "Just because you don't see them does not mean that they are not there. Many hide under leaf litter and debris or burrow into the sand and mud.
"Even if you do not step on the animals, it is stressful for them just trying to avoid you."
Bukit Batok Nature Park
This small nameless stream runs along the southern edge of the Bukit Batok Nature Park and winds through the forest.
It can be seen at three points along the forest track, where it flows under three small bridges.
The closest you can get to the water is at the Southern Plaza area, where people can go right up to its muddy edges.
When The Straits Times visited, there were fish, dragonflies and tadpoles in the water and a pair of waterhens.
Most of the fish in the water are introduced species and were most likely released by pet owners, says Dr Darren Yeo, an assistant professor of biology at the National University of Singapore.
These species include whitespot (Aplocheilus lineatus), guppies and mollies.
So far, they do not appear invasive, that is, they have not wiped out other native species, says Dr Yeo.
Some native species which can be seen there are a fish called whitespot (Aplocheilus panchax) and a dragonfly called the spine-tufted skimmer (Orthetrum chrysis).
When you visit the stream, it is possible to make an excursion to the rest of the nature park, which sits on a hill.
Bukit Batok Nature Park was once mined for granite in the 1900s and there is a quarry with a huge reflecting pool.
If you are good with steps, also visit the remains of a war memorial at the top of the hill.
The memorial was built by the Japanese to commemorate those who died during a fierce battle on the hill during World War II.
The memorial's structure, which included a shrine, has since been destroyed. All that is left are the steps leading to the shrine and two short pillars at the base of the staircase.
Now, at the top of the hill is the Mediacorp Transmission Centre.
• For more information on these trails, go to www.nparks.gov.sg/gardens-parks-and-nature/walks-and-tours/going-on-a-diy-walk
Petaling Stream near TreeTop Walk
This stream near the end of the Petaling Trail belongs to a network of streams near TreeTop Walk in MacRitchie that drains into the MacRitchie Reservoir.
The TreeTop Walk trail starts from Venus Drive and takes about three hours to complete. The Petaling Stream comes into view at the end of the trail just after the TreeTop Walk and runs under the boardwalk.
Looking down from the boardwalk, you can spot small fishes at the surface of the water, snacking on insects that had fallen from the surrounding vegetation.
The fish include the white spot (Aplocheilus panchax), distinguished by an iridescent spot on the top of its head, Malayan pygmy halfpeak (Dermogenys collettei), a fish with a lower jaw that sticks out like a sharp snout, and the saddle barb (Systomus banksi), which can be recognised by a dark blotch on its back and sides.
Dragonflies abound, too. Perching on plants or flitting around, these pretty, hovering creatures come in shades of pink and red.
The common parasol (Neurothemis fluctuans) has a maroon body and wings.
The spine-tufted skimmer (Orthetrum chrysis) has a red body and black wings, while the crimson dropwing (Trithemis aurora) has a pink body and reddish- pink wings.
Dragonflies are common in forest streams as their larvae or nymphs are fully aquatic, says Dr Darren Yeo, an assistant professor of biology at the National University of Singapore.
He says: "They live underwater and can help control the population of mosquitoes by feeding on mosquito larvae."
Madam Low Cheng Yee, 44, who was at the trail with her twin sons, aged nine, says they would make a point to stop at the stream for at least 10 minutes every time they pass by.
Madam Low, who is self- employed, says: "It's very rare to see a natural stream in Singapore. I find it very relaxing to look at it while my sons love to spot fish and insects such as dragonflies."
Stream at Lower Peirce
This nameless stream, which runs along part of the Cyathea Trail boardwalk before it drains into the Lower Peirce Reservoir, is a hub of social activity for all sorts of creatures.
On good days, kingfishers, sunbirds, forest birds, monitor lizards and even mousedeer can be seen going to the stream to hunt, bathe or take a sip of water.
There are three ways to access this stream along Old Upper Thomson Road: from the Lower Peirce Reservoir Park, the Casuarina or Jacaranda Entrance. It is a walk of about 15 to 20 minutes from each entrance.
For the most scenic route, take the entrance from the reservoir park. Follow a boardwalk to the edge of the reservoir, just next to the water.
Here, the view of the reservoir is framed by the greenery of the Central Catchment Nature Reserve.
Then the boardwalk enters the forest and splits into a few trails. Take the Bamboo Trail, which will lead you to the Cyathea Trail, where the forest stream is.