The first time we scouted the Tsangpo, in late April, the river had already started to rise. We walked away from it. It was much bigger than we'd ever imagined. We just sat there saying, "There's no way."

Once we'd figured out it was potentially runnable, we hit the books. The biggest issue was scale. We were looking at aerial photos from the 1920s, some walking expeditions, and a little bit of video. But nothing really translated: What looked like medium-size boulders turned out to be house-size boulders.

Alpha dog? There were a lot of decisions to be made. It takes a strong person who knows what they're doing and will still be respected. It's the same as any leadership position.

Now I'm waiting for things to mellow out between Pakistan and India so we can complete the last section of the Indus, the last of the four rivers—I've already run the Karnali, the Sutlej, and, of course, the Tsangpo—that flow in the four cardinal directions off of Mount Kailas. The Tsangpo was the most formidable of the bunch, but together they're the biggest, baddest rivers in the Himalayas.