Lake Tonle Sap: The Endangered Heart of Cambodia

Every spring, the monsoon swells Cambodia’s Tonle Sap Lake, part of the lower Mekong basin, up to five times its dry-season size. The people here live in floating villages that rise and fall with the water. For centuries, they have welcomed the floods, because the floods bring fish—a catch of about 300,000 tons—and they bring nutrient rich sediment for flood-plain cropland and support an incredibly diverse ecosystem, including several endangered species.

But the Tonle Sap is under threat. The lake suffers from overfishing. The flooded forests, a nursery for young fish, are being cut down for fuel and farmland. A changing climate will likely bring more extremes of flood and drought. And more than a hundred hydropower dams have been built or are planned upstream on the Mekong, threatening the flood pulse, sediment flow, and fish migration.

There are no easy answers. The pressures on the Tonle Sap cross borders, highlight difficult trade-offs in natural-resource use, and play out in a web of connections between people and nature that’s rife with unintended consequences. An international group of scientists is working with the local residents and Cambodian authorities to solve this puzzle. They’re building a massive, dynamic computer model of the lake’s ecosystem—from the chemical mix of its soils to the markets for its resources—one that can hopefully forecast the tradeoffs and surprises and plot a way through the maze of threats. There’s no guarantee of success. However, as the planet warms, the dams rise, and more fish species vanish, both time and options are limited.

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Tonle Sap Lake is one of the most productive freshwater ecosystems in the world. But overfishing, climate change and plans to build a hydropower dams could threaten the delicate ecosystem.

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