The river flows intermittently, usually flooding in late summer; the rest of the year it becomes a chain of long narrow pools.

About 650 million years ago (Mya), plate movement had formed a north-south graben, or lowered area, along which the ancient Fish River could flow and eventually erode a flat plain to create today's upper canyon.

About 60 Mya, South America and Africa separated (due to continental drift) and Africa rose significantly; the consequentially increased gradient of the Fish River enabled it to erode the lower canyon into the hard gneisses, forming the current deeply twisting, meandering system of the lower canyon.

The immense scale and rugged terrain has drawn many visitors from all over the world to experience hiking or trail running the canyon.

Extreme weather, such as flash floods, stormy winds and rain occasionally play havoc during the hiking season.

[6] Due to flooding and extremely hot summer temperatures reaching 48 °C during the day and 30 °C at night, permits are only issued between 1 May and 15 September.

[7] Prior to arriving at Hobas a hiking permit must be obtained from Namibia Wildlife Resorts[8] for groups not smaller than 3 and not larger than 30.

All hikers must be older than 12 years[7] and a certificate of fitness, completed by a medical doctor, must be presented at the offices of the Ministry of Environment and Tourism at Hobas.

Popular short cuts are found at: The river flows stronger early in the season and by September usually dries up to form a chain of stagnant pools.

The route starts close to Hobas and after a short section on the rim of the canyon steeply descends 500 meters to river level.

Due to the remoteness of the trail, all competitors are required to be self-sufficient for the duration of the event and are expected to have adequate nutrients as well as the stipulated survival gear.

Previous trail runners have commented on the difficulty of the terrain: "The canyon is one of the most beautiful places I have seen but at the same time is one of the harshest environments I have run in.