Tonle Sap Lake | Aqua Expeditions

Life on the Tonle Sap Lake

3 years ago Culture, Mekong, Nature

Since the beginning of history, the Tonle Sap lake and river system has been a source of abundance that nourished a population of more than one million at the height of the empire in the 12th century

Back in the days of the glittering Angkor era, the Tonlé Sap lake and river, which branches off the Mekong river in today’s Cambodia, was to the Khmer empire what the Nile river was to the Egyptians.

Enriched by the freshwater flowing down from the Tibetan plateau, the Tonle Sap lake assured the Khmer people that they never had to worry about running out of food and water, even though their numbers had amounted to 0.1 percent of the world population at the time!


With their sustenance fulfilled, the people of the ancient Khmer metropolis were free — in both mind and body — to pursue and develop artistic pursuits that included silk weaving and silversmithing, finessing a flavorsome local cuisine, as well as planning and building grand monuments like the Angkor Wat.


The Angkor Wat in Cambodia

The Angkor Wat in Cambodia

Today, many from far and wide flock to present-day Siem Reap to witness the astonishing level of culture forged by the Khmer people, but only a few realise there is more to the Tonle Sap itself than first meets the eye. In fact, locals often claim that a Cambodia trip would be incomplete without being on the Tonlé Sap, for Cambodia and her cultural treasures would never have existed without it.



An endless giver of life, the Tonle Sap Lake is also a spectacle of nature. To better understand it geologically, it’s easier to liken the lake to a giant bathtub. For the majority of the year, the Mekong River flows 2,700-mile (4,350 km) southwards from the Tibetan highlands to the South China Sea, and the Tonle Sap’s water empties into the Mekong.


Tonle Sap in the Low Water Season

Tonle Sap in the Low Water Season

But as monsoon winds from the southwest bring higher rainfall to other parts of Southeast Asia between May and October, the Mekong River begins to swell. By around June, the Mekong would have risen to a level that forces the Tonle Sap river to flow backwards into its own lake.


In fact, the Tonle Sap is the only river in the world that flows both ways seasonally, reversing direction twice a year. As the river flow flips from a downstream to an upstream direction, the Tonle Sap lake starts to fill up at an instant, bringing along millions of fish from the Mekong and allowing river ships to enter. Suddenly, the thousands of amazingly tall stilted houses that perch on what resembles a swamp make perfect sense. By September, the water level of the Tonle Sap lake would have increased to more than 4 times its original depth.


Kayaking the Tonle Sap in the High Water Season with Aqua Expediitons

Kayaking the Tonle Sap in the High Water Season with Aqua Expeditions. In Khmer, ‘Tonle’ means freshwater and ‘Sap’ means lake.

Since the Tonle Sap lake has no other outlet, the inflow from the river also expands the lake to more than four times its normal area, from approximately 1,050 square miles to 4,500 square miles at its peak! For about five months every year, the Tonle Sap Lake can lay claim to the title of the largest freshwater lake in Southeast Asia.


Tonle Sap Map

Map of Tonle Sap with satellite imagery showing the difference in area between Low- and High-water Seasons.

As the annual waters rise, large area of what was originally forest and shrub land become inundated, providing excellent breeding and feeding grounds for newly arrived fish, including carp and catfish. This is called the high-water season. When the waters drop, some fish survive in small, remnant ponds on the floodplain, providing easy pickings for fishermen.


In fact, the Tonle Sap is one of the most productive fishing lakes in the world, supporting over three million people and providing over 75 percent of Cambodia’s annual inland fish catch and 60 percent of Cambodians’ protein intake. Its fish species richness and productivity is ranked fourth in the world.


The phenomenon of water flowing upstream towards Siem Reap also enabled the architectural feats of the Khmer empire that would otherwise have been impossible to build. Historical records showed that the Khmer cleverly harnessed the upstream river currents to transport the quarried stones needed to build Angkor’s great temples, including the Angkor Wat.


Finally, every November, when the pressure of the Mekong is relieved, the Tonle Sap once again reverses its course. This time, the reversal is marked with big fanfare in Phnom Penh’s three-day Water Festival. Called Bon Om Touk in the Khmer language, the festival sees colorful traditional longboat races take place on the riverbanks of the Tonle Sap in Phnom Penh, the Cambodian capital, a hark back to the days of the Angkorian empire eight centuries ago and a tribute to the great king Jayavarman VII.




Even though the influx of water is a greater spectacle, the slow exhale of the Tonle Sap’s lake has been just as important in the history of Cambodia. It’s during this time that farmers in the area can ‘trap’ the retreating river to irrigate crops, with enough water to enable the harvesting of up to three crops a year when only one would be possible elsewhere.



In the high-water season, when the Tonle Sap lake is accessible by cruise ship, this is the best time to discover a fascinating façade of Cambodian culture that is brought to vivid life on water.


Better still if your Mekong cruise ship carries a reliable fleet of launch boats that serve as starting points for excursions to the more undiscovered communities of the Tonle Sap, which are typically located further away from Siem Reap (i.e. at the opposite bank of the lake).


Out of the 3 million people living in and around the Tonle Sap lake, 90 percent earn a living or are dependant on fishing or agriculture. Considered non-immigrant foreigners, made up of three ethnic groups Vietnamese, Cham and Khmer, they are the “forgotten people” or people without a homeland.


Divided into several communities, these lake inhabitants have formed around a hundred small villages floating on the Tonle Sap. Living in “floating villages” on either stilted homes or houseboats accessible only by water, villagers can be found in their long sampans out in the day, using bamboo fish raps to catch fish. Adapting completely to the nature of the environment they live in, locals spend most of their lives floating on the water. This water is their primary source of life and food and their home. The fascination of a floating existence attracts many tourists to witness the unique lifestyle in the Tonle Sap villages.  


The small communities living on the lake represent a combination of movable houses and permanent structures. The movable houses comprise the floating villages, and they can be relocated when the water levels rise. The stilted villages, on the other hand, are made to be permanent structures. The tall, thin stilts hold the house high enough, keeping the household dry during the wet season. Moreover, the very long ladders are made to reach the water when the level is low, making for an interesting sight during the dry season.


Another common sight: Schoolchildren getting into a bit of squeeze, four or five of them, onboard a single sampan — embarking on a regular after-school joy ride that looks like the very definition of freedom.


Tonle Sap Family

A family on the Tonle Sap.

A skiff or kayaking tour of Tonle Sap’s floating villages unravels a culturally significant, yet a seldom-seen side of Cambodian life. As your guide charts a path down waterways, you soon realize you can no longer anticipate what you’ll be seeing next. It could be a floating church, a family with a dozen children, or an ice factory that you’d feel compelled to disembark to explore. Be prepared to be pleasantly surprised at every turn.


Perhaps the most intriguing of floating villages on the Tonle Sap lake is Moat Khla, where we take guests on skiffs to a floating Buddhist temple set amidst tranquil greenery (of trees whose trunks have been submerged by the high waters).


Theravada Buddhism has been the dominant religion of Cambodia since the 13th century at the height of the Khmer empire. Speaking to humble, saffron-robed monks about their faith at the floating temple, you might come away with a new perspective on life — or simply a feel-good lightness after attending the blessing ceremony!


Moat Khla Blessing Ceremony

A Buddhist Blessing Ceremony at Moat Khla, Tonle Sap.



Aside from those seeking and finding spirituality, birdwatchers aren’t left out either. With the abundance of fish swept upstream into the Tonle Sap Lake during the high-water season, an entire ecosystem of birds tags along. In 1997, the Tonle Sap was officially recognized as a UNESCO Biosphere Reserve for its unique wetland habitat that supports a large seasonal population of waterbirds.


Spot-billed pelican Cambodia Tonle Sap

Spot-billed pelican (Pelecanus philippensis) in flight

The Tonle Sap Biosphere Reserve is split into three key protected areas known as biospheres. Of the three biospheres, Prek Toal (to the Northwest of the Tonle Sap) is arguably the most stunning. A bird lover’s dream, the Prek Toal Bird Sanctuary Biosphere Reserve is regarded as the single most important breeding ground for globally threatened large waterbirds such as the Black-headed Ibis, Painted Stork, Greater and Lesser Adjutants, Spot-billed Pelican, Milky Stork and the Grey-Headed Fish Eagle.


As is often the case, who you sail with determines how rewarding your Prek Toal excursion would be. Sailing into this vast, 121-square mile biosphere on a speedy, low-emission, ergonomically-designed aluminum launch boats privately owned and maintained by the cruise line, with a knowledgable guide in tow, is perhaps the most ideal. (We’re the only Mekong cruise line with its own private skiffs, complete with sun-shielding canopies on top!)


Tonle Sap Birdwatching with Aqua Expeditions

Guided birdwatching on the Tonle Sap on board an Aqua Expeditions skiff.

Even though we know Prek Toal like the back of our hands, it’s still awe-inspiring to realize that the large network of ‘shrubs’ — that seemingly floating on the lake — are actually canopies of massive trees that have been submerged by the swelling waters of the Mekong. It’s not uncommon to see hundreds of large birds of various species perching on these canopies like a festival is taking place.

Here lies the challenge: Our guests are sometimes so engrossed looking into their binoculars that we have to say “Take care! Don’t move forward, or you’ll fall into the water!”

Clearly, the Tonle Sap isn’t just a blessing for the locals. To visitors from far and wide, this is an extraordinary example of nature that keeps on giving; an inspiring ensemble of sight, sounds, experiences that add to an already distinctive, culturally rich Mekong river cruise.


The Aqua Mekong sails into the Tonle Sap Lake from August to December every year. Dates may vary.


Discover our Mekong trip highlights, our itineraries, and the award-winning Aqua Mekong cruise ship.