I met Rob Wilson when I was 15. He was the trip leader on my first commercial river guide job on the Orange River in South Africa, a mighty drainage that tumbles down the slopes of the Lesotho in the Drakensberg Mountains 2,000 kilometers before emptying into the Atlantic.

I next ran into Rob on the banks of the Orange in 2009, when he was paddling the river from source to sea, during his "Pure Orange Expedition." A few months later he invited me to join him and his partner, Ine, for a four-day descent of the Augrabies Gorge, a rarely run 30-kilometer section of the Orange. The gorge is rarely run because you have to rappel into it. Our first abseil dropped us and our gear into a canyon of house-sized boulders. The size of the terrain was overwhelming. The mercury pushed up over 100, sweat dripped from my face and my lips tasted like a salt pan. We set up a zipline for the boats, followed by another abseil from a tree branch. It felt awfully dodgy. We camped in the canyon that night, enjoying a well-earned ration of cous cous.

At daybreak we watched the sunlight creep through the gorge corners and light up the granite walls. Everyone was excited for coffee, but our stove wasn't playing along. We missed our morning caffeine fix, but the adrenaline would soon make up for it.

We moved down the steeper section of the gorge where the rapids were bigger than anticipated. At one of the biggest Class Vs, Rob and I paddled while Ine stayed on the bank looking after safety and shooting stills. I followed Rob down the long entry weaving between boulders. I eddied out and when I glanced over my shoulder, I saw an orange boat upside down.

Ine signaled that Rob was swimming, and I chased after him. As soon as the current caught my boat, I realized this rapid was much bolder than I'd expected. It was no wonder that Rob had been pushed off line with his heavy boat. I paddled through a lateral wave and down a steep tongue into a hole. It nearly stopped me, but somehow I got through and caught a glimpse of Rob giving the all-safe signal from the bank. He had a few bumps and bruises but got back on his horse. After the last rapid we hid in the shade, where the stove finally cooperated. Night fell as we sipped coffee and admired the endless African sky glittering above.

Scott Martin is a South African photographer. Rob Wilson and Ine Skjorten are writing a guidebook to the Senqu, Orange and Gariep river systems.