“Live bait.” 

That’s what today’s training is called. More properly, “tethered rescue” — an advanced swift-water technique for rescuing unresponsive victims from whitewater situations. The rescuer swims aggressively into fast-moving water in a specialized life jacket, tethered by a rope to a second rescuer on shore. The swimmer catches the victim and is swung back to shore by their partner. If anything goes haywire, the rescuer can pull a quick-release ripcord, be free of the tethering rope and move on to Plan B. It’s complicated, it’s tricky, and if you haven’t trained to do it, it’s dangerous. But it’s also incredibly effective, so we practice it. Over and over and over.

We’re on a guide-training trip with Canyon Explorations and Canyoneers, two of the dozen or so Grand Canyon river operators. Swift-water training is but one of many fields we’re covering: geology, biology and archaeology...