Why do Khone Falls make navigation on the Mekong River difficult?

The Khone Falls are the primary obstacle to navigation on the Mekong River because they consist of a massive, double series of cataracts that create a physical barrier between the river's northern and southern sections.12

Caused by a resistant bed of basalt, the river tumbles 45 feet (14 meters) over these falls, preventing continuous water transport between Laos to the north and the Cambodian plain to the south. Due to this significant impediment, the falls have historically limited the economic use of the river, necessitating alternative methods such as portaging goods or using a narrow-gauge railway to bypass the area. While smaller vessels can navigate parts of the river downstream, the Khone Falls—along with other falls located between Sâmbor and Pakxé—effectively block through-traffic, restricting upstream navigation to local use.12