One of the most formidable impediments to full navigation of the Mekong is the mighty Khone Phapeng Falls near the Cambodian border – the largest in Southeast Asia, and a jaw-dropping spectacle, especially during the rainy season. Beyond the cataracts, the river divides into a tangle of different channels, flowing for roughly 30 miles (50km), around a constellation of islets and islands. The so-called Si Phan Don, or ‘Four-Thousand Islands’ region supports a population of rice subsistence farmers, whose paddy fields form splashes of brilliant green against the dun-coloured river banks.