Where a River Flows Backward

BY AWAKE! WRITER IN CAMBODIA

HAVE you ever seen a river flowing backward? How about a forest that is underwater for half the year? Did you know that people live in floating houses that must be moved because the water disappears? “Impossible,” you say? If so, you may change your mind after a visit to Cambodia during the monsoon, or rainy season.

Each day, from mid-May through October, clear morning skies darken and in the afternoon shed their load of rain. Water cascades over formerly dry and dusty ground, and rivers burst their banks.

Why Backward?

Look at the accompanying map. Notice the spot where the mighty Mekong River meets the Tonle Sap River. The waters merge and soon divide into the Mekong River proper and the Bassac River. They then continue flowing southward through the country of Vietnam, forming the giant Mekong Delta.

Soon after the rainy season begins, the lower reaches of the delta flood. The surging waters inundate seasonally dry tributaries. As the monsoon continues, the Tonle Sap River backs up and begins to flow northward, instead of following its usual path to the south. In this way the flooded river flows backward until it pours into Tonle Sap Lake.

This lake is located in a shallow plain approximately 65 miles [100 km] from Phnom Penh, the capital of Cambodia. During the dry season, the surface area of the lake is about 1,000 square miles [3,000 sq km]. In the wet season, however, water swells the surface area to four or five times its usual size, making the lake the largest body of freshwater in Southeast Asia.

Areas that were once home to rice paddies, roads, trees, and villages are now swamped. Fishermen, whose boats used to float in water only three feet [1 m] deep, glide over the tops of trees up to 30 feet [10 m] tall! Elsewhere, such widespread flooding is usually viewed as a disaster. But to the people of Cambodia, it is often considered a blessing. Why?

When Flooding Is a Blessing

The backward-flowing Tonle Sap River deposits rich layers of alluvial sediment in the Tonle Sap basin. In addition, massive numbers of fish swim up into the lake from the Mekong River and spawn in the nutrient-rich environment. In fact, Tonle Sap Lake is one of the world’s richest sources of freshwater fish. After the wet season, the lake empties so fast that fishermen have been known to pick stranded fish from the trees!

This annual flooding creates a dynamic ecosystem. Trees and other vegetation within the floodplain adopt a different growth cycle from plants in nonflooded areas. Normally, tropical trees grow slowly, shedding leaves in the dry season and then sprouting new growth during the wet. In contrast, trees in the Tonle Sap region do not shed leaves until they are submerged by the flooding rains. And instead of the growth rate increasing during the wet season, it slows. After the water subsides and the dry season begins, branches sprout buds and leaves grow quickly. When the lake empties, the ground is covered with a layer of decomposing foliage that nourishes trees and other plant life during the ensuing dry season.

Living on Stilts and Floating Platforms

What about the people? Some lake dwellers build their small homes on stilts. During  the dry season, these houses are up to 20 feet [6 m] above the ground. But during the time of peak flooding, fishing boats and large metal bowls that are sometimes used to transport children dock right at the doorstep.

Other lake dwellers live on a type of houseboat, building their homes on floating platforms. When the family grows, an additional floating platform is attached and the home extended. There are an estimated 170 floating villages on the lake.

During the day, young and old are on the water using fishing traps and nets. As the water level rises or falls, houses or entire villages may move several miles in order to remain close to the new shoreline or to more-productive fishing areas.

Long canoes become grocery stores or floating markets, supplying the various daily needs of the community, even serving as public “buses.” Children who attend school go to a floating schoolhouse. Everything, from plants to people, moves to the rhythm of the water in the land where the river flows backward.

[Map on page 23]

(For fully formatted text, see publication)

Dry season

Wet season

CAMBODIA

Tonle Sap Lake

Tonle Sap River

Mekong River

PHNOM PENH

Bassac River

Mekong Delta

VIETNAM

[Picture on page 23]

A boy paddling along the Tonle Sap River

[Pictures on page 23]

Photos of the same village​—in dry season and wet season

[Picture Credit Lines on page 23]

Map: Based on NASA/​Visible Earth imagery; village photos: FAO/​Gordon Sharpless