“There’s a chance we’ll flip on this section,” says Kade Hertz, our captain. “If anyone would like to switch to the safety raft, now’s your chance.” No one says anything. I’m a strong swimmer, but the rapids ahead look terrifying: Gallons of white water unfurl violently, wrapping around boulders the size of cars and opening up enormous swirling black holes. Still, we jam our feet into our rubber footholds, straighten our backs, and paddle forward, ice-cold water already pooling at our feet.