A Priceless Environmental Treasure

The Tonlé Sap Lake in Cambodia is your new favorite wildlife sanctuary



As the car left the sealed road and bumped off onto the deeply rutted, heavily scarred track, it became clear that this route

would be un-passable at the wrong time of year — at least in a road vehicle. During the rainy season, vast swathes of this area undergo seasonal flooding, and boats are the only way to get around. I was on my way to Prek Toal Bird Sanctuary, on the Tonlé Sap Lake in Cambodia.


A spot-billed pelican at Prek Toal Bird Sanctuary.

Most people visiting the town of Siem Reap in Cambodia head there for one reason — the fabulous temple complex of Angkor Wat — the oldest and largest religious monument in the world. It is true that no trip to this part of Cambodia would be complete without spending a couple of days visiting Angkor’s various temples. There is the main temple of Angkor Wat itself, the famous, strangler fig-encrusted Tha Phrom temple, as well as some of the more far-flung sites, such as the ancient Roluos Group of temple ruins.


For nature lovers, however, there is another reason to spend a few more days in the area. Located about two hours’ drive from Siem Reap, next to the Tonlé Sap Lake, Prek Toal Bird Sanctuary is home to many rare bird species, some of which breed in just one or two spots around the world. Many of these birds are migratory, and the best time for bird watchers is the dry season, which offers the greatest number and variety of birds.


Prek Toal floating village, Cambodia.

The nearby Prek Toal floating village is also located on the Tonlé Sap Lake. During the dry season (December–April) parts of the village remain floating on the lake, but come the rainy season (May–November) the whole village transforms, and the reason for the tall stilts on which some of the permanent buildings stand becomes obvious.


A stilted house, Prek Toal.

A must-see for bird watchers


In 2015, as Southeast Asia’s largest waterbird breeding colony, Prek Toal was designated a Wetland of International Importance (also known as a ‘Ramsar site’, after the Iranian city where the intergovernmental treaty, the Convention on Wetlands, was signed). The bird sanctuary is home, for part of the year at least, to an incredible variety of birds, many of which are increasingly rare. For example, the spot-billed pelican (Pelecanus philippensis) is a near-threatened species which currently has breeding areas in just three locations around the world, Tonlé Sap Lake being one of them. Rarer still is the greater adjutant (Leptoptilos dubius), an enormous stork that grows up to 1.5 metres tall, of which there are thought to be just 1,200 breeding pairs remaining in the wild.


Greater adjutants looking for food.

Flocks of Indian cormorants (Phalacrocorax fuscicollis) spend their time alternating between diving for fish one minute, and sunning themselves, wings outstretched, on a convenient tree top the next. Wading around in the shallows are striking purple swamphens (Porphyrio porphyrio). There are Oriental darters (Anhinga melanogaster), little egrets (Egretta garzetta), and Brahminy kites (Haliastur indus), along with various species of colourful bee-eaters. Even those who are not bird lovers cannot fail to be impressed by the sheer abundance and variety of avian life at Prek Toal.


Purple swamphens nervously patrol the shallows.

A unique ecosystem


The area’s unusual ecosystem stems from the yearly seasonal rains and a unique relationship between the Mekong River and the Tonlé Sap Lake. During the rainy season, the Mekong rages and surges with additional water from monsoon rains and Himalayan snowmelt. This forces water to flood into the Tonlé Sap Lake, via a river also known as Tonlé Sap. This flooding causes the lake to increase in area by up to five times, inundating areas which only weeks before had been dry and dusty, temporarily making Tonlé Sap the largest freshwater lake in Southeast Asia. It also gives rise to the famous ‘flooded forests’ of the region, when it is possible to kayak between the treetops, only their twisted, uppermost branches visible above the waterline. As the rains come to an end, the floodwaters recede, and the waters flow back out, via the Tonlé Sap River, into the Mekong River. As the waters pass into and out of the lake, huge numbers of quick-spawning, rapidly growing fish provide plentiful food for all local inhabitants. This pulse of the two rivers and the lake is known locally as the ‘heartbeat of Cambodia’, such is its importance for humans and wildlife alike.


A painted stork perches in the tree tops.

The future of the Tonlé Sap ecosystem


There are numerous threats facing this unique ecosystem. Dams built for hydropower projects, upstream on the Mekong River, could have serious impacts on fish migration and other aspects of the lake’s ecology. Climate change is reducing glacier size in the Himalayan headwaters that supply the Mekong, affecting water volumes, and this is likely to affect the river basin as a whole, with resulting deleterious effects on the biodiversity of aquatic communities living there. Invasive species like water hyacinth also pose a major threat to aquatic life and make navigation more difficult for fishermen and others who ply the local waterways.


Sunset over Prek Toal floating village.

Visitor information


It is possible to visit Prek Toal Bird Sanctuary on a day trip from Siem Reap — many tour operators offer such a trip. However, I would highly recommend spending at least a couple of days there, and one of the best ways to do that is with a homestay in Prek Toal floating village. This leaves plenty of time for bird-watching, as well as exploring the village itself. You can sit in a floating restaurant and watch village life unfold, with local children in boats, rowing themselves to school; fruit sellers paddling their way from house to house, selling their wares; even a monk giving blessings from a passing boat. I can highly recommend the company I travelled with, Osmose Ecotours, who run responsible, community-based eco-tours, employ local people from the village, and are committed to local community development in Prek Toal.


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