THE MEKONG IS the 12th-longest river in the world, traveling nearly 2,600 mile (4,200 kilometer) from its source in the Tibetan plateau to its enormous delta in southern Vietnam. It is the major transportation highway and supplier of life for most of Southeast Asia—with 5 cities over 100,000 and one-third of the populations of Thailand, Laos, Cambodia, and Vietnam (60 million people) in the lower Mekong basin—yet much of it is still undeveloped (the first bridge was built in 1993, between Thailand and Laos) and even unexplored (the source was located definitively only in 1994). This is due to the torturous path the Mekong cuts through rough mountain terrain on its journey from the Tanggula Mountains in China to the South China Sea. It changes names many times along the way, from Lancang Jiang (“turbulent river”) in China, to Mae Khong (“mother of waters”) in Laos and Thailand, Tonle Thom (“great water”) in Cambodia, and Tien Giang or Cuu Long (“river of 9 dragons,” for the delta’s many channels) in Vietnam. The river is navigable by seagoing vessels as far as Phnom Penh, the capital of Cambodia, a distance of 340 mile (550 kilometer), but they are prevented from going much further upstream by numerous sandbanks and rapids. Communities upriver use smaller vessels on the river, in some places the only route for communications and transport of goods. European powers were excited by the possibility of using the Mekong as a passage to the riches of the interior of China, which never materialized. The French established a protectorate over the kingdom of Laos in the 1860s (in haste, to beat the British) before fully exploring this option, however, and were disappointed by the river’s limited capability for commercial transport in the interior. Laos was therefore mostly ignored as a colony (benign neglect), and remains 1 of the most underdeveloped nations in the world. The 1990s witnessed a burst of hydroelectric projects (23 are planned in Laos alone), generating a good deal of international protests, because of the enormous impact these projects will have on the ecology of the region and the lives of millions of its inhabitants. The Mekong River Commission, based in Phnom Penh, predicts dire consequences for rice production and the fishing industry in the lower basin, which accounts for about 2 percent of the world’s total. Manwan Dam in Yunnan Province (China), for example, will radically alter the course of the river, preventing downriver annual flooding essential to the production of rice. Regional governments ignore these warnings, however, seeing the projects as major symbols of their countries’ modernity. The Mekong originates near the roof of the world, in the Jifu Mountains (about 17,160 foot or 5,200 meter), near the town of Zadoi on the borders between the Chinese provinces of Xizang (Tibet) and Qinghai. Here the small mountain river moves swiftly through barren chasms and gorges. The river flows south into Yunnan province through narrow gorges, only a few kilometers from the parallel valleys of the upper Salween and Yangzi (Changjiang) rivers, which ultimately end their courses thousands of kilometers away in the Bay of Bengal and the East China Sea, respectively. The river then flows from China into the valley separating eastern Myanmar from Laos, which has served as a conduit for Chinese migration into Southeast Asia. Thousands of Chinese emigrated to Mandalay in Myanmar, where they now dominate commercial life. This route is also a passage for illegal arms shipments from China and for drugs (opium and heroin) into China. The Mekong then forms the main corridor of settlement for the lowland Lao peoples, first in the interior of the country, then along its border with Thailand. One of the oldest cities in the region, Loang Prabang, was established on its banks in the 14th century, followed by a rival Buddhist kingdom centered at Vientiane (Viangchan), about 250 mile (400 kilometer) downriver. Loang Prabang retains much of its beautiful architecture, Buddhist temples, and French colonial buildings and has recently been classified as a World Heritage Site. Below Pakxé (Laos), the Mekong becomes much wider, and, after the dramatic drop at Khone Falls on the border with Cambodia, enters the wide, flat Cambodian plain. Thousands of years ago, this plain was at the bottom of the sea, but material brought downstream from the mountains gradually filled it in to form a fertile plain, with numerous confluent rivers and large lakes. The largest of these lakes, Tonle Sap, is the remaining evidence of the sea’s onetime incursion into this area. The lake is formed by 1 of the rivers that flow into the Mekong, which reverses course from backflow during the rainy season, expanding the lake up to 6 times its normal size. This area, with its natural irrigation systems and fertile soils, was home to many early civilizations in Southeast Asia, including the empire of the Khmers with its famous temples at Angkor Wat. The Mekong delta starts in Cambodia and extends 175 mile (282 kilometer) to the sea. Forming a vast alluvial plain (called the Plain of Reeds), it is the heartland of southern Vietnam, covering 26,000 square mile (67,340 square kilometer). The river splits into 2 main channels, and numerous smaller passages, forming a broad delta on the South China Sea. The delta was the site of many powerful civilizations, notably the Cambodian kingdom of Funan, which was a busy entrepot between Chinese and Indian civilizations as early as the 3d century C.E. (even Roman coins have been discovered here). Commercial wet-rice production was established by the French colonial powers from the middle of the 19th century. It was the economic center of the former South Vietnam, and remains 1 of the most densely populated areas in Southeast Asia. As independent nations, the countries bordering the Mekong River have struggled to coordinate activities and to limit destructive overdevelopment in the production of rice and logging. Since 1957, regional associations have proposed numerous projects for hydroelectric power, navigation, and flood control, but wars and political turmoil have allowed few to become a reality. Much of the area remains very poor and very rural, relying on rice farming and subsistence fishing.