As China celebrates the 60th anniversary of Communist Party rule, there are many signs of the country's growing international influence. One of the least recognised is its role as Asia's dominant headwater power.
Geography has made China the source of some of the most important rivers that flow into South and Southeast Asia. They include two of South Asia's great rivers, the Indus and Brahmaputra, and two of Southeast Asia's - the Salween and Mekong. All have their headwaters on China's Qinghai-Tibetan plateau. These four great rivers flow for much of their early course through Chinese territory.
For Southeast Asia, by far the most important is the Mekong. In 1986, when China began building the first of a series of dams on its section of the Mekong, hardly anyone in downstream countries paid attention. But today, as China races to finish the fourth hydroelectric dam on the river's upper reaches, concerns are rising in the region about the possible environmental impact.
The sheer scale of China's engineering is setting off alarm bells in Vietnam, Cambodia, Thailand and Laos, the four countries of the lower Mekong basin where more than 60 million people depend on the river for food, water and transport.
A report in May by the United Nations Environment Programme and the Asian Institute of Technology warned that China's plan for a cascade of eight dams on the Mekong might pose 'a considerable threat' to the river and its natural riches. In June, Thailand's prime minister was handed a petition calling for a halt to dam building. It was signed by more than 11,000 people, many of them farmers and fishermen who live along the river and its tributaries.
Some analysts say that, if the worst fears of critics are realised, relations between China and its neighbours in Southeast Asia will be severely damaged. But, mindful of the growing power and influence of China, Southeast Asian governments have muffled their concern.
Meanwhile, Laos, Cambodia and Thailand have put forward plans to dam their sections of the Mekong, prompting objections from Vietnam and undermining the local activists' case against China.