The boats leave from a pier below the ticket office, on the riverside just north of the main street, and they run on an economics all their own. A boatman will not push off for a single passenger. Two fares is the minimum, so a lone traveller in a hurry pays double and effectively buys the empty seat beside them - about 40,000 kip to Don Det rather than 20,000, on 2023 prices. Wait, and someone will turn up. That is the whole system: no timetable, just a slow accretion of people on a bank until the arithmetic works. After half past five the fare rises, and after eight in the evening the boats stop altogether. Miss that window and the islands, visible across the water, might as well be a day's travel away.

Nakasang exists because Don Det and Don Khon are islands, and islands run short of things. This is the nearest large market, and it works the way river markets do - busy from dawn through the early afternoon, then thinning out as the heat settles. The stalls run along the bank, so goods come off the boats and onto the tables with barely a change of hands. There are ATMs now, across the street from the bus station, which for years was the single most useful sentence in any guidebook covering the region: the islands themselves had none, and travellers routinely got stranded by their own cash. Places to eat cluster near the water, most of them serving Lao food, most of that noodle soup. Several guesthouses take the overflow. Arriving from the Cambodian border a few hours south, the town can seem almost cosmopolitan - which says more about the road than about Nakasang.

A few kilometres downstream, the Mekong does something spectacular and inconvenient. The Khone Phapheng Falls are not tall - the maximum drop is about 21 metres - but they are the widest waterfall on Earth, spread across 10,783 metres of river, with rapids running for nearly ten kilometres. The average discharge through them approaches 11,000 cubic metres per second, and floods have pushed that past 49,000. They are the single reason the Mekong cannot be navigated from the sea into China. French colonial engineers tried in the late nineteenth century, failed, and settled for a workaround: a seven-kilometre narrow-gauge railway across Don Det and Don Khon, opened in 1893, over which whole boats were hauled from one navigable reach to the next. It closed in the 1940s. The rails are gone, the bridge between the two islands survives, and the boats from Nakasang are the direct descendants of that failure.

Leaving is governed by a clock as unforgiving as the boats'. The last public bus to Pakse pulls out of the market at around ten in the morning; the private service booked from an agent on Don Det comes through about quarter to twelve. After that, the day is spent whether you meant it to be or not. The town is small enough to cross on foot in a few minutes, though the walk out to the main highway is long and hot enough to regret. So people sit. They drink something cold, watch the loading and unloading, and look across at the islands. The Irrawaddy dolphins that once surfaced in these pools are gone now, the last of them found dead in early 2022. What remains is the river, the boats, and a town that has quietly organised its whole existence around other people's arrivals and departures.