"The Khone Falls is the prime reason why the Mekong river is not fully navigable into China" and the most impressive waterfall I've seen even though really it's more a cascade of rapids rather than a waterfall. "The highest falls reach to 21 metres (69 ft); the succession of rapids stretch 9.7 km (6.0 mi) of the river's length. The average discharge of the cataract is nearly 11,000 m3/s (390,000 cu ft/s), with the highest flow on record at over 49,000 m3/s (1,700,000 cu ft/s)." See Wikipedia
