How Can Cambodia Sustain Its Freshwater ‘Fish Factory’?

CI marine biologist Les Kaufman spends most of his trips to the “field” near, on or in the ocean. But this week in Cambodia’s Tonle Sap region, he’s in for something different. Les is part of a team studying the interactions between one of the world’s largest freshwater fisheries and the people who depend on it.

fish in Cambodian marketplace near Tonle Sap

A combination of native and exotic fish caught in the Tonle Sap, for sale at Siem Reap marketplace. (© CI/photo by Les Kaufman)

As our plane zoomed in over the lake, we could see the vast lake floor spreading from horizon to horizon. At the moment, the lake’s low water levels were settled into the deepest fifth of the land it occupies during flood season. The waters were dotted by stilted and floating villages; vast rice systems ringing the lake stretched from its floodplains to year-round terra firma.

The monsoons are just beginning anew, so the afternoon sky is bedecked with big boomers (thunderheads) all about. Tonle Sap — the Great Lake — is a monstrous engine of rice and fish, diversity and life. CI is here, working with our Cambodian partners, to stem the disappearance of this world.

Blighted by poverty, corruption, climate change and dams, yet buoyed by tradition and deep national pride, Tonle Sap — the largest lake in Southeast Asia — has been aptly called the beating heart of Cambodia. We want to see it keep on beating.

view of Tonle Sap, Cambodia, from the plane

View of Tonle Sap from the plane. (© CI/photo by Les Kaufman)

Tonle Sap is just one important part of the larger Mekong Basin ecosystem. This region hosts over 1,000 species of freshwater fishes alone, not to mention an extraordinary array of freshwater snails; profusions of waterbirds (including several of special concern); the world’s most exuberant inland fishery; and troubled giants such as the vanishing giant Mekong catfish, giant barb, giant goonch and giant stingray.

Surrounding hills harbor hyperdiverse tropical forests once coursed by elephant, tiger, rhinoceros, wild cattle and a host of equally charismatic creatures. It is a storied mix of land and water at the center of millennia of imperial turmoil. Two hundred fish species frequent the Great Lake alone, flowing from it into surrounding markets and households. This diet has traditionally been supplemented by rice in several thousand varieties; very few of these are still commonly available.

This wealth has attracted people to the lake shore over centuries, fueling the rise and inviting the fall of great empires — most famously the Angkorian culture and its central icon, the Angkor Wat temple complex. Tonle Sap’s colorful history now generates a new form of wealth as tourists from all over the world — more than a million strong each year — flock to the region in the stately company of pelicans, storks and egrets.

The secret of Tonle Sap’s vitality lies in a massive pulse of monsoon floodwaters that swell the lake to five times its dry season size, opening up forest labyrinths as spawning, feeding and nursery grounds for the fishes and other animals. However, without swift conservation action, Tonle Sap is headed for trouble.

Fishing pressure is extremely high, yet the system incredibly fecund, which may have led many to think that this “fish factory” might actually be invulnerable to continued reckless plunder. Protected areas exist, but resources for enforcement are modest and unable to stem the flowering of illegal fishing, logging and poaching of wildlife.

fruit vendors at Siem Reap marketplace, Cambodia

Fruit vendors at the Siem Reap marketplace. (© CI/photo by Les Kaufman)

In addition, the lake’s pulse-flow dynamic is now under imminent threat from global climate change, and from a profusion of dams — hundreds now planned — that are sprouting throughout the northern reaches and tributaries of the Mekong Basin. The goal of these dams is ostensibly to generate clean power. However, no massive warping of natural system dynamics can be all that clean, and the changing Tonle Sap offers graphic evidence.

What are viable futures for the people of Cambodia’s heartland? Are there ways forward that are capable of both sustaining human existence in the short term, and ensuring the survival of Tonle Sap’s stupendous biological diversity? Our goal is to find out.

Les Kaufman is a marine conservation fellow with CI and a biology professor with Boston University. Read the next blog in this series from his Tonle Sap trip.


  1. Leonardo Saenz says

    Hi Les, very inspiring blog. Tonle Sap is one of those places that should be sacred and remained untouched. It seems like there is a need to gain some time in order to show the potential consequences on nature and people of affecting the crucial regimes you describe from climate change or dams, before they are irreversibly transformed by the latter. Is there any chance to gain some time to better discuss these issues among regional authorities, political or private sectors? Leo

    1. Les Kaufman says

      Hi Leo, thanks. Since only a few of the 200 or so dams planned for the greater Mekong System are already in place, yes, there is still time to amend what will ultimately become the overall water management system for the Mekong Basin, including Tonle Sap. There is also time to assist the residents of the Tonle Sap region in developing adaptation strategies for coping with the changes that have already begun to take hold, as well as those to come. There are two keys to this business- first, that much that has gone wrong with Tonle Sap actually predates the dams or climate change, and two (flip side of the same thing), since 30% of the waters that flood the Tonle Sap Basin each year derive from surrounding watersheds, there is substantial marginal benefit to be gained from better managing just that portion of the Mekong…something that residents can actually have some say in. With pressure for hydropower mounting, especially in China, local returns on local investments can matter a great deal. The situation is not simple- the flood in the Mekong main stem delivers 70% of Tonle Sap’s floodwaters and serves as the critical plug containing the flood that expands the lake, working its miracles. However, just as we can be creative in messing things up, we can turn this same ingenuity to keeping ecosystem functions intact.

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