Vietnam has an enormous number of rivers that are at least partly navigable, but the most important by far is the Mekong River and its tributaries. Scenic day trips by boat are possible on rivers in Hoi An, Danang, Hue, Tarn Coc and even HCMC, but only in the Mekong Delta are boats used as a practical means of transport.

Boat trips are also possible on the sea - a cruise to the islands off the coast of Nha Trang is a particularly popular trip. If you visit Halong Bay, a cruise to the islands in that region is a must.
 In some parts of Vietnam, particularly the Mekong Delta, there are frequent ferry crossings. Don't stand between parked vehicles on the ferry as they can roll and you could wind up as the meat in the sandwich.