Si Phan Don — "Four Thousand Islands" in Lao — is where the Mekong loses its shape. At the southern tip of Laos, just short of the Cambodian border, the river swells to fourteen kilometres across and shatters into a maze of channels, rocky shoals and palm-topped islets. The name overstates the count, but not the feeling: hundreds of sandbars surface as the water drops in the dry season, and about half of them disappear again when the monsoon floods the river. At the foot of the archipelago the whole Mekong tips over Khone Phapheng, the highest-volume waterfall in Southeast Asia — a barrier so complete that no boat has ever run the river from the sea up into China. Three islands anchor the sprawl: Don Khong, large and farming-quiet; Don Det, long a byword for cheap riverside hammocks; and Don Khon, keeper of the French colonial relics.
Life here runs at the river's pace. There are almost no cars. You cross between Don Det and Don Khon on a century-old French railway bridge, and pedal red-dirt paths past rice paddies and wooden stilt houses. At dusk the light turns the Mekong copper and water buffalo wade in to cool off. Wooden longtails thread the channels to sandbars where you may not meet another soul, and the Li Phi falls churn white through the forest on Don Khon. The river also carries a harder story: the deep pool at the Cambodian border was the last home of Laos's Irrawaddy dolphins, and the country has none left. A rusting 1911 steam locomotive still waits at Ban Khon, the relic of the only railway the French ever laid in Laos.