Nam Ngum is a sprawling artificial lake about 90 kilometres north of Vientiane, formed when the Nam Ngum River was dammed in the 1970s for what became one of Laos's first and most important hydroelectric projects. The reservoir flooded a wide valley, and the drowned forest left behind gives the lake its strange, memorable character: hundreds of small islands rise from the water, and bleached tree trunks still jut from the surface in the shallower reaches. It is the easiest big-landscape day trip from the capital, and on a clear day the combination of green hills, open water, and floating timber is genuinely striking.
The usual way to see the lake is by boat. Operators at the main landing run trips out among the islands, and you can negotiate anything from a short loop to a half-day on the water. A couple of the larger islands have been turned into low-key resorts and restaurants, and the floating and shoreside eateries are known for fresh fish straight from the reservoir — grilled tilapia and Lao-style fish soups are the things to order. It makes for an unhurried day: a boat ride, a long lunch by the water, and the trip back.
Getting here is simplest with your own transport or a hired car and driver, since the lake spreads across a rural area with scattered access points and the boat landings are not all easy to reach by public bus. If you do go by bus, take an early departure from Vientiane's main bus station toward Talat or the dam, and allow plenty of time for the return. Most visitors fold Nam Ngum into a longer day that also takes in Vang Xang or breaks the journey toward Vang Vieng.