MEKONG ECOLOGY THREATENED BY SILTATION, DEFORESTATION

* In one of the world's oddest ecological wonders, the Mekong River becomes so flooded in the rainy season that it forces its major tributary to reverse course and expand a lake, the Tonle Sap, to four times its size.

But these days, this natural phenomenon near Phnom Penh is in jeopardy due to the siltation caused by the river, which is caused by a rapid rise in the felling of forests in Cambodia.

``It's very sad. All we can do is slow down the deforestation,'' says the Mekong Committee's environmental expert, Lars Neilsson. ``Within 10 years, the forests in the Mekong [basin] will disappear.''

One consequence is a protein shortage in the diet for almost all Cambodians. The Tonle Sap, which provides much of the nation's fish, is now difficult to reach for those fish that swim up from the Mekong each year to spawn in the lake. They cannot get past the rising silt bars in the river.

The Cambodian government recently began dredging operations to try to fix the problem. The silt buildup has also forced many ocean-going vessels, coming up the Mekong from the delta, to unload their cargo at Phnom Penh during the dry season.

As peace came to the region, large-scale logging of Cambodia's forests, led by Thai and Japanese companies, began in the late 1980s. But in Vietnam's highlands, too, the forest cover has been cut to 56 percent. In the delta, the forest cover has decreased 50 percent since 1970 due to reclamation and war.

Thailand, Laos, and Cambodia have tried to ban the export of logs in the hopes of saving the watershed, but smugglers still operate in remote areas.

Even though demands on the Mekong region's resources are relatively limited compared to other Asian rivers, it is facing a number of environmental crises.

In the delta, for instance, many Vietnamese farmers have switched to lucrative shrimp farming, destroying mangrove swamps and increasing the threat of salt water on farmland.

A number of ``salt dams'' have been built to stem the intrusion, which threatens Vietnam's ``rice bowl.'' The delta's unusual acidic soil also poses problems for farming as the level of the Mekong fluctuates irregularly.