The Karangarua River flows almost entirely within Westland Tai Poutini National Park on New Zealand's South Island, a designation that has significant implications for access. Because the river sits within a national park, helicopter landings are prohibited throughout most of its length. The one exception is a designated landing zone at Christmas Hut, located at the headwaters of the river, which serves as the practical starting point for expeditions into the upper section.

The upper Karangarua offers approximately 12km of whitewater that remained unrun until relatively recently, situated more than 20km into a wilderness zone. The upper gorge is characterized as extremely steep, though the riverbed reportedly provides sufficient room to maneuver and scout at river level throughout. A location known as Cassel Flat marks a notable point along the river where the upper and lower sections effectively meet. The lower section of the river had been paddled prior to the upper section's first descent.

Given the remoteness, the national park restrictions on helicopter access (outside the Christmas Hut landing zone), and the steep technical nature of the upper section, this is a serious multi-day wilderness undertaking suited only to highly experienced expedition paddlers. The combination of difficult logistics, remote terrain, and challenging whitewater means that thorough planning and scouting are essential before committing to a full descent.