Tonle Sap—Cambodia’s pulsing heart

A fisherman on the lake.

A fisherman on the Great Lake.

Cambodia’s Tonle Sap river connects Southeast Asia’s largest lake — Tonle Sap or Great lake — with the majestic Mekong. Twice a year a remarkable phenomenon, the reversal of its water flow, occurs in this watercourse.
During the cool and hot season it flows from the lake to the Mekong, but when the monsoon rains raise the water level of the Mekong by metres, its volume pushes up into the Tonle Sap River and drains into the Great Lake.

Consequently, the Mekong water inundates extensive areas beyond the lake’s dry season extent of about 3,000 square kilometres, at least doubling its size. But in November, when the rains have stopped, the flow of the Tonle Sap River reverses again, and the Great Lake gradually releases much of its volume back into the Mekong.

In Phnom Penh this reversal of the Tonle Sap River’s water flow is traditionally celebrated with fireworks and boat races. In November 1901, French writer Pierre Loti — a celebrity in his lifetime — witnessed the festivities from “one of the royal junks the prow of which represents the enormous head of some monster from a Cambodian dream.” Later on, he writes, “Long racing galleys go past in a furious eddy of spray…maniulated by half-naked men, who paddle standing, with striking postures, shouting encouraging cries.”

Basrelief Bayon.

Fish and crocodiles in the Tonle Sap are depicted in bas reliefs of the Bayon.

As this reversing current is the key to the region’s natural wealth — an abundance of fish and fertile paddies — it is no wonder  the event is celebrated with so much zest.

Hundreds of square kilometres of forests are annually submerged and become an ideal feeding ground  for spawning fish. Then, when the water recedes from the inundated cultivated areas, a sediment of fertile mud is left behind, its nutrients replenishing the soil that guarantee a rich harvest. Consequently, it is easy to grow rice all around the lake, while the Tonle Sap itself is one of the world’s most productive inland fishing waters. It seems likely these natural blessings contributed to the rise of the ancient Khmer empire, since its capital Angkor was built just north of the Great Lake.

Basreliefs Bayon.

Bas reliefs of the Bayon showing a war vessel on the Great Lake and an abundance of fish.

At Angkor’s magnificent Bayon — a major shrine erected during the reign of Jayavarman VII — the southern wall’s bas-reliefs contain numerous scenes from a twelfth century naval battle on the lake. Below the boats of the Cham invaders and the Khmer defenders swim numerous large fish, densely packed in the shallow water. Such a concentration of fish was not merely an artistic convention, since the French naturalist Henri Mouhot, who crossed the lake seven centuries later, observed “the fish in it are so incredibly abundant that they are actually crushed under the boats, frequently impeding the play of the oars.”

Almost two hundred species of fish occur in the lake, of which the carp and catfish can grow to a respectable one hundred kilogrammes. The Chinese envoy Chou Ta-Kuan, who visited Angkor from 1296 to 1297, reported that black and other kinds of carp, tenches and fresh-water congers were commercially most important. But the lake was also teeming with other water creatures. “The prawns weigh as much as a pound a piece. Flippers of tortoises…are eight or nine inches long. Crocodiles there are large as boats, which have four feet and are exactly like dragons, with no horns however. Their belly is delicious to eat. In the Great Lake it is possible to fish out by hand bivalves and gastropodes.” At least one crocodile is depicted  on the Bayon’s bas-reliefs, hungrily devouring a wounded warrior who has fallen from one of the war barges.


Bayon relief with croc and fish

A Bayon relief with fish, crocodile, crab and turtle.

Chou Ta-Kuan also mentioned the fertile lands around the lake. “No use is made of human dung [as in China]…and generally speaking, three or four crops a year can be accounted for…From the fourth to ninth moon there is rain every afternoon, and the level of the Great Lake may rise seven to eight fathoms. People living at the water-side leave for the hills.” And he noticed a “certain kind of land where the rice grows naturally, without sowing,” probably referring to floating rice varieties. “When the water is up one fathom, the rice keeps pace in its growth.”

Although growing rice was easy aound the lake, most of it was actually grown in the millions of small, bunded fields located at higher elevations than the flood plains. These fields depend completely on the monsoon rains. Such rainfed agriculture limits the output to one rice harvest a year, and is still commonly practised in much of Cambodia, as well as in Northeast and Central Thailand.

After crossing the lake, Mouhot visited Angkor’s splendid ruins. His lively descriptions of them were soon followed by the romantic drawings  made by L. Delaporte, a member of the French Mekong expedition. Europeans became fascinated by the ‘lost exotic civilization’ of the Khmers and their magnificent monuments. Research of the ruins started at the end of the century, and not much later it was widely believed that the Khmer empire had been a “hydraulic state”. The giant water works in and around Angkor, such as the baray (reservoirs) and moats, were supposed to be part of an elaborate irrigation system. Some of the former are of truly impressive size — the West and East Baray each measure seven by two kilometres — while the moats around Angkor Wat are a hundred metres wide.


Sras Sang

Angkor's Sras Sang. Whatever its function, the large reservoir was useless for irrigation of the fields.

Until recently ‘Angkor’s irrigation system’ has been one of the less disputed and most repeated assumptions (‘mantras’, historian Michael Vickery would say) in modern history. In a now classic article published in 1980, Dutcha agricultural engineer W. J. Van Liere showed the fallacy of such supposed irrigation works. His reasonng is simple: without the employment of costly energy, water flows downwards. As Angkor’s baray and moats are situated at a lower level than the bunded rice fields, they could not have served for the irrigation of these fields. Van Liere also argues, that no feeder canals from the baray to the fields have been found in the archaeological record. Furthermore, there is not even any indirect evidence of such a large irrigation system. Nor is any mention of it made in the extensive corpus of ancient stone inscriptions. And even Chou Ta-Kuan does not say anything about it, although he commented on almost everything remarkable — from how Khmer women bath and the way incest is punished, to the preparation of fermented drinks and the method of caulking the boats.

Many historians now wisely agree with Van Liere, but the ‘hydraulic state’ is still an article of faith in the popular literature. Even the decline of the Khmer civilization has been attributed to the neglect of these supposed irrigation works.

floating houses

Vietnamese pedlars paddling their ware to the floating houses on the Great Lake.

However, the ancient Khmers did take advantage of a giant, natural irrigation system — the annual rise and fall of the Tonle Sap — and the abundance of fish that results from it.

Next to Angkor’s most reknown temples, such as Angkor Wat, Bayon, Tha Phrom, and the more remote Banteay Srei, a sightseeing boat trip on the lake has become a major tourist attraction. Daily, busloads of tourists are shuttled to the lakeside south of Siem Reap to get an impression of the colourful fishing industry. Fish provide sixty percent of the Cambodian pupulation’s protein intake, and a major part of this is hauled from the lake. The pungent smell of drying fish that greets the visitor near the lakeside and the many jars full of fermenting fish along the roadside are testimony to this fact.

At high water, the small boats leave from the foot of the Phnom Krom (Krom Hill), from the top of which one has a superp view of the immense Great Lake. But during low water, one has to continue the bumpy ride for another five kilometres to get to a place where the creek is deep enough for the small fishing and pleasure boats to moor. The dusty road is flanked by palm leaf huts built on stilts, a picturesque but poor marginalised community — the remnants of families of government soldiers, once stationed in the area to fight to Khmer Rouge.

Stilt houses along the lake shore.

Stilt houses along the Great Lake's shore.

On a standard trip, a small boat will navigate the creek towards the mangrove-clad rim of the lake. Many floating houseboats line the route, mostly homes of fishermen. There are also numerous bamboo rafts used to dry small fish, to unload holds full of mollusks, or to store and repair hundreds of fish and crab traps.

Men standing in the shallows cast their nets into the creek. Loads of small fish are carried ashore in large baskets of plaited bamboo. Everywhere fishermen are repairing their nets, while piles of bamboo fence sections lie waiting to be taken out on the lake there to be pounded into the mud. The form part of the ingeniously designed fish traps, each comprised of kilometres of bamboo screens laid out in a maze to confuse the swimming patterns of the fish. This is actually the most lucrative fishing method — the trapped fish are herded to extraction points and once or twive a week the catch is hauled in by net and shipped to the fresh markets.

One also passes floating schools where the pupils arrive in tiny paddle boats. As the creek gets wider, and slightly deeper, one enters a floating village, encompassing groceries, barber shops, dealers in grated ice, gas stations and even floating churches. And everywhere are fish in underwater cages.


Bamboo fences pounded in the mud of the lake guide the fish to the large traps.

model trap system

A model of a large trap with bamboo fences.

Most of the inhabitants are Vietnamese, attracted to the lake’s wealth of fish. Already in Mouhot’s day, Vietnamese fishing communities flourished on and along the lake. When Pol Pot’s Khmer Rouge rose to power in 1975, all Vietnamese were deported to their country.  But in the 1980s, they returned. Unfortunately, strong anti-Vietnamese sentiments have survived the Khmer Rouge, and even recently, a number of Vietnamese habe been killed  in occasional flurries of envy and hate.

Usually a boat trip includes a stop at a crocodile farm in the lake. The crocodiles are raised for their leather, and are fed with snakes — in the morning, before the arrival of the tourists. Some farms exhibit models of the elaborate fish traps. Anyway, from there one can easily see the kilometres of bamboo screens that form the fish traps scattered around the shallow lake.

Angkor Wat

Angkor Wat's huge moats did not serve the irrigation of the fields.

Another, larger Vietnamese floating village, Kompong Luong, is on the other side of the lake. At the town of Krakor, where a dirt track branches off Highway 5, an odd looking signboard is testamony to the special character of the roads around the Tonle Sap:




In one of the Cambodian national birth legends, the natural retreat of the lake’s waters is attributed to the magic power of a naga king. It tells of the arrival of a prince from India, named Kambu, who married the daughter of the naga (serpent spirit) king who ruiled over the land that was to become Cambodia. Approving of their union, the naga king drank down the waters in a mighty draught, thus draining the lake and creating the land where the couple were to live.

©SJON HAUSER: text and images.