With roughly 4600km of navigable waterways, rivers are the ancient highways of mountainous Laos. The main routes link Houayxai to Louang Phabang and Pakxe with Si Phan Don, all of them along the Mekong River. Smaller boats regularly cruise up the wide Nam Ou River, linking Louang Phabang to Nong Khiaw and Phongsali, and a weekly vessel still manages the trickier Louang Phabang-to-Vientiane route, a journey that can take nearly a week.

The long, narrow diesel-chugging slow boats ( heua sa) that ply these routes are built to fit the maximum amount of cargo and do not have any seats, leaving passengers to grab any spot they can find on the floor. Male passengers often opt to sit on the roof - an option not available to women because of Lao customs . You can never be guaranteed that there'll be a boat on a certain day, so show up early in the morning and ask around. Given fluctuations in current, and lengthy stops to load cargo, boats sometimes don't make their final destination during the daytime, forcing passengers to sleep in the nearest village or aboard the boat. Such stops will take you off the tourist track, so it's a good idea to bring extra water and food. Travel by slow boat can be dangerous and reports of boats sinking are not uncommon. The Mekong has some particularly tricky stretches, with narrow channels threading through rapids and past whirlpools, and can be particularly rough late in the rainy season.

On the northern routes , tickets are sold and ports overseen by a local government official. Foreigners pay significantly more than locals, but fares are generally posted. Buy your ticket the day you leave. Southern routes are more haphazard: prices are not posted and it's unlikely that you'll need to buy a ticket in advance.

Pesky, fire-engine red speedboats ( heua wai) are Laos's version of adventure travel, and a riskier, more expensive alternative to the plodding cargo boats. Connecting towns along the Nam Ou and the Mekong from Vientiane to the Chinese border, these five-metre-long terrors can accommodate up to eight diminutive passengers. They can shave hours or days off a river journey, but cost as much as two to three times the slow-boat fare. Crash helmets are handed out before journeys: the headgear is meant to spare your hearing from the overpowering screech of the engine - not your head. However, you should still consider bringing along earplugs. Some drivers also provide life jackets. It's by no means safe, of course, although captains swear by their navigational skills. In one particularly nasty accident in 1998, two boats collided head-on, killing all on board.