BANGKOK, Thailand -- Midway through its epic 5,000-kilometer journey from the Tibetan Plateau to the South China Sea, the Mekong River forms the border between Laos and northeast Thailand.

The Mekong River, fed by a series of tributaries, flows for 4,900 kilometres from its source in the Tibetan plateau through China, Myanmar, Laos, Cambodia and Vietnam to the sea.

Cambodia and China have signed a $1.2 billion deal to finance an ambitious canal project that aims to boost trade efficiency ...