 In 1994, he led an expedition to locate the elusive source of the Mekong River, following the Dza Nak (the black Mekong, the historical main branch of the river), believing that he had discovered the source of Asia's third longest river.Ten years later, a Sino-Japanese expedition proved that the geographical source (the farthest from the sea) lies at the headwaters of the white Mekong, Dza Kar, which satellite photos show to be 4500 meters longer than what Peissel called the historical branch.Thus, like the Mississippi, the Yellow and countless other rivers, the Mekong is considered to have a geographical source and a historical source.