Water levels on Southeast Asia's longest river, the Mekong, have fallen to their lowest level in 40 years, threatening the livelihoods of millions of people in the six countries along its banks, RFA's Vietnamese and Mandarin services report.
"On March 18, the river's water level was down to only 90 cms. Now, it's raised a little but it's still very low," one villager from Chiang Rai in northern Thailand told RFA's Vietnamese service.
Data from the Mekong River Committee's Web site show the water level, measured at Vietnam's Chau Doc station on March 20, was 80 cms, decreasing to just 40 cms on March 25.
Experts up and down the Mekong — ; known as Lancang Jiang in Chinese, Lang Thuong in Vietnamese and Mae Nam Khong in Lao and Thai — ; say they are concerned at the possible effects on agriculture, the fishing industry, and transportation links of low, and widely fluctuating, water levels.
High levels of salt water, or salination, are now being found in higher reaches of the river than before, affecting the use of land for farming. And lower-than-ever water levels mean that fish don't have enough water to lay eggs and replenish stocks.
According to local media reports, salination levels reached 1,800 mg per liter in March 2004, or 0.18 percent, compared with just 300 mg per liter for the same period in 2002.
"The problem with seawater entering Cuu Long Delta — ; there are many factors, but the two main factors are the flow volume and the area of land under cultivation," U.S.-based hydrology expert Nguyen Minh Quang told RFA's Vietnamese service. He used the Vietnamese name for the Mekong where it enters that country.
This year's drought has meant less fresh water flowing out to sea, meaning that the seawater penetrates higher up the river after tidal flows, Nguyen Minh Quang said, adding that more intensive agriculture in the area had also had its effect.
"Before there were irrigation systems such as holding pools or dams, when the tides entered the river, it spread out evenly. Therefore the degree of saltiness remained low and it did not enter deeply into the rivers," he said. "Now that there are dams and holding pools to drain, it causes the flow to be restricted. The tidal waters enter deeper into the rivers because of the flow restrictions."
China is frequently held responsible by its neighbors for decreased water flows further down the Mekong. But Chinese ecologists and engineers told RFA's Mandarin service that upstream dams are not the only factor affecting the river.
"This includes factors like the weather," Sichuan-based rivers expert Yang Xin said. "Other factors include the increasing demand from people's daily needs, industrial development, and agricultural development."
Hydropower expert Wu Yegang said the building of dams should not be rejected entirely, but the pros and cons should be comprehensively considered.
"Of course, we need to do our best to minimize the building of dams because each dam has a huge effect on the environment and the ecology," Wu said. "The consequences are more and more serious. Also, we still don't understand many of the consequences. In light of this, the building of a dam right now should be a very cautious affair with many feasibility studies," he added.
China's leadership has recently backed away from plans to develop a series of thirteen hydroelectric dams on the Nu River, which had drawn concerns from downstream Burma. The planned 21-kilowatt project was shelved after widespread opposition from academics and experts from around the country.
The Mekong River is more than 4,200 kms long. Springing from a source on a Tibetan plateau 5,000 feet above sea level, the lower half of the river runs through Burma, Thailand, Laos, Cambodia, and Vietnam, where it splits into the Tien Giang and Hau Giang, entering the Pacific Ocean via nine estuaries.
Its name, which derives from the Thai and Lao Mae Nam Khong, means "mother of all rivers."