While there are continuing uncertainties as to whether a dam is going to be built on the mainstream of the Mekong at Xayaburi in Laos, Chinese authorities have just announced that the major dam at Nuozhadu on the upper reaches of the Mekong in Yunnan province has started generating electricity. 

Nuozhadu is the fifth Chinese dam to be commissioned in Yunnan and it will ultimately have a generating capacity of 5500MW. For the moment only one of its nine generators is functioning, but all will be in operation in 2014. Like the already completed dam at Xiaowan (pictured), Nuozhadu has been built on an huge scale, with a dam wall rising 261m and a reservoir that will eventually cover 320sq km.

The official announcement in the China Daily is of more than passing interest, for two reasons. First, because it speaks of the newly operating dam as being one of seven Chinese dams on the upper section of the river lying within Chinese territory (it has previously been widely accepted that there would eventually be eight dams) and because it again repeats the claim that the Chinese cascade of dams will not effect downstream countries because only 13.5% of the water in the Mekong as a whole flows through China.

This claim has been discredited many times over, as I noted in my Lowy Paper, River at Risk.

Water from China is of great importance in sustaining dry season flow for the downstream countries, perhaps to a total of 40% of the river's volume overall. So with each dam China builds there is the prospect of a greater diminishing of the flow, particularly as both Xiaowan and Nuozhadu will act as storage dams rather than having a 'run of the river' character.

There is no doubt that the commissioning of five dams in Yunnan province will have other long-term effects downstream, not least in relation to the amount of nutrient-rich sediment flowing down the river. There is also the likelihood that Cambodia's Great Lake (Tonle Sap) will be reduced in area during the wet season, to the detriment of its current vital role as a source of much of Cambodia's protein consumption through its vast bounty of fish. 

China's Mekong dams are so remote they receive little coverage in the Western media. Yet, like the more readily viewed sites for proposed dams in Laos and Cambodia, what is happening in China will eventually alter the productive capabilities of mainland Southeast Asia's longest and most important river, a river vital to the sustenance of the 60 million people of the Lower Mekong Basin.

Photo by Flickr user International Rivers.