Did Cambodia's Most Famous River Stop Changing Course?
To fill up the Tonle Sap lake, its river reverses course twice a year. But droughts and dams appear to have stilled the unique phenomenon.
by Abby Seiff
October 16, 2020, 8:00am
Not far from Cambodia's famed Angkor Wat temples, the towering stilts keeping wooden houses at safe levels above water have been rendered useless — the land below is dry.
It's September, the height of rainy season, and these floating villages on the upper edge of the Tonle Sap lake should be flooded. But something has gone wrong. The eponymous river that pushes billions of gallons of water into the lake each rainy season has gone still. The lake, which expands and contracts like a beating heart twice each year for millennia has barely spilled past its dry season borders.
"We don’t see the water rising up like before," said Kheav Cheam, a 50-year-old fisherman. "In the past, the water rose higher and spilled into the lake, so we could catch fish. But now, the water doesn't go into the lake and the fish don't grow bigger."
In Cambodia, fish is the main source of protein for as much as 80 percent of the population. Cheam, who lives with his family in a small boat that they move between the river and the lake, has survived off these waters his entire adult life. Now, he often fails to catch enough to offset the cost of gasoline. "We're afraid that people living in the upper parts have closed the dam, so we are growing desperate. It's getting worse and worse for fishing — in the future, there will be no fishing, because there is no water left."
The Tonle Sap lake is the largest body of freshwater in all of Southeast Asia and one of the most successful inland fisheries in the world. Its productivity comes from a unique hydrological function. The lake is fed by the Tonle Sap river, a Mekong tributary that reverses course twice a year, sending water, nutrients, and migrating fish down from the upper reaches of Asia's mighty Mekong river into the lake and back again. The first reversal typically takes place in May, as the Mekong swells with rain, forcing water into the Tonle Sap river and up into the lake. By November, the volume of the lake has grown so large it exerts an opposite force, sending water back down the eponymous river and into the Mekong.
This flood pulse that feeds Cambodia's Tonle Sap can expand the lake up to six times its size — as much as 6,000 square miles — during the rainy season. With it comes fish, an extraordinary abundance that has sustained the population for thousands of years. Ancient lakeside tombs hold the remains of cooked meals: fish salted and marinated; fish turned into soup; fish roasted and smoked. Angkorian bas reliefs are studded with snakeheads and carps and vendors selling freshly caught fish. "There are very many fish whose names I don’t know, all of them coming from the Freshwater Sea ... They get clams, mud clams and pond snails just by scooping them out of the Freshwater Sea," Zhou Daguan, a Chinese emissary who penned the first outsider's account of Cambodia, wrote in the late 13th century. Today, some 500,000 tons of fish are pulled from the lake each year, and millions more from the rest of the lower Mekong basin, which spreads across neighboring Thailand, Laos, and Vietnam. With the flood pulse slowing, the fish are fast vanishing.
Last year, the Tonle Sap river reversal occurred months later than usual and lasted barely six weeks. This year, some believe it never reversed course at all. If it did, climate change and dams have left the river level so low as to make the reversal negligible.
Usually, the reversal lasts 160 days and sends 38.37 cubic-kilometers of water flooding into the lake, according to two-decade averages collected by the Mekong River Commission, an intergovernmental body aimed at joint river management. An MRC report released at the end of September shows a staggering drop. During July, August, and September, the lake reached a quarter of its normal volume. In fact, the lake's volume during that time was barely half of what it was a year earlier — when the Mekong receded to a historic low, leading to food shortages across the region.
Monitoring from the Mekong River Commission shows that water levels on the Tonle Sap river in September were about half their average depth. At the end of September, the river approaches its maximum height: it's typically some 8.5 meters deep at Phnom Penh Port, which sits at the bottom of the Tonle Sap river, less than a mile from where it meets the Mekong. This year, it was 4.4 meters.
Until mid-October, as a tropical storm and flash flooding battered Cambodia, the height of the Tonle Sap river never once topped 5 meters — a depth, that if sustained, serves as the tipping point at which the river would reverse course, according to Brian Eyler, Southeast Asia program director at the Stimson Center.
Full article and photos:
https://www.vice.com/en/article/dy8gv7/ ... ing-course