The latest finger pointing at China comes in the wake of devastating floods in parts of northern Thailand and Laos after the Mekong, South-East Asia's largest river, overflowed its banks, inundating villages and rice fields, and leaving a swath of destruction that will cost many millions of dollars to repair.

The water level on August 15 at Vientiane, the capital of Laos on the banks of the Mekong, was the highest since records began in 1913. Although it has dropped since then, low-lying regions in Cambodia and the Mekong Delta of southern Vietnam are bracing themselves for similar damage as the floodwaters move downstream.

Some Thais hit by the floods, as well as non-governmental organisations campaigning against dam building, say that water released from the reservoirs of three big Chinese dams on the upper reaches of the Mekong swelled the runoff from a tropical storm and heavy monsoon rain across northern Laos and China's southern Yunnan Province early last month.

But the Mekong River Commission, in a statement last week, pointed out that the volume of releasable water held by the three Chinese hydro-power dams to generate electricity was too small to have been a significant factor in the flooding. The commission, established by the governments of Cambodia, Laos, Thailand and Vietnam in 1995 at the end of a long period of conflict in the region, helps to coordinate management of the Mekong Basin in South-East Asia.

As the world's 12th longest river, the Mekong runs through or between six countries China, Burma and the four commission member states. Although the Mekong starts high in China's Qinghai-Tibetan plateau and flows through China for more than one-third of its total length of over 4300km, China is not a commission member.

Nor is reclusive Burma. They are ''dialogue partners'' who meet commission members from time to time and share only some information about their respective sections of the river.

The commission says that the combined storage capacity of the three Chinese dams on the upper section of the Mekong is less than one cubic kilometre. It adds that only a small part of this could have been released as the floodwaters in the area accumulated between August 8, when the tropical storm struck, and August 12, when the flood peak in the Mekong was measured at Chiang Saen, in Thailand, where the commission has its most northerly monitoring station.

At Chiang Saen on that day, measurements showed an accumulated flood runoff volume for the month of 8.5 cubic kilometres, while further downsteam at Vientiane on 12 August it was 23 cubic kilometres, leading the commission to conclude that any release from the Chinese dams ''could not have been a significant factor in this natural flood event''.

While this may be true, Chinese dam construction on the upper reaches of the Mekong is a legitimate source of concern for downstream South-East Asian countries. To generate electricity, water has to be released to drive the turbines.

Their worry is that too much will be released in the wet season, contributing to flooding, and too little in the dry season, when the water is needed in South-East Asia.

This concern will be accentuated when China completes the fourth dam on its section of the Mekong by 2013.

This dam at Xiaowan will be 292m high, one of the world's tallest. It will generate over 4000 megawatts of electricity, the equivalent output of at least four nuclear power stations.

Its reservoir will impound water in a 190sqkm reservoir that Chinese officials say will hold 15 billion cubic metres of water, nearly five times the volume held by the three existing dams.

They say this will reduce the amount of water flowing into South-East Asia by 17 per cent during the flood season and increase the flow by 40 per cent in the dry season.

Four more dams are planned for the Mekong in Yunnan, one of which will have a storage capacity similar to Xiaowan. Just filling the Xiaowan dam's reservoir is estimated to take between five and 10 years, using half the upper Mekong's flow. Clearly, a cascade of dams on this scale will affect the amount and quality of water available to downstream states in South-East Asia.

Averaged over the year, only about 20 per cent of the water flowing into the lower section of the Mekong comes from China. However, Chinese policy is particularly important in the dry season, when the long stretch of the Mekong on its territory accounts for 50 per cent to 70 per cent of the water flow at the mouth of river in Vietnam, where it meets the South China Sea.

If China is serious when it promises a cooperative and mutually beneficial partnership with South-East Asia, it should join the Mekong River Commission as a full member, share all hydrological information with its neighbours and integrate its Yunnan dam planning into the development blueprint for the lower Mekong Basin.

This would strengthen commission efforts to develop and apply an integrated management plan for the whole of the Mekong River Basin, with multilateral as well as national interests in mind.

The writer, a former Asia editor of the International Herald Tribune, is an energy and security specialist at the Institute of South-East Asian Studies in Singapore.