A man sits on the bow of a boat as it heads upriver at sunrise along the Mekong River in Kampong Cham. The Mekong is the largest river in Southeast Asia and the 12th longest river in the world. From its source in the Tibetan Plateau the river runs 4,350km across 6 countries to the South China Sea, and has been a vital trade route for thousands of years. - Kampong Cham, Cambodia I spent 6 years backpacking around the world to 94 countries and several months along the route of the Mekong river.