Aerial photographs from the 1950s didn’t prepare Adam Shoalts for what he was about to encounter. The self-dubbed “modern explorer” was canoeing a stretch of little-known whitewater rapids just south of Hudson Bay when the river started to disappear in front of him. Courtesy: Adam Shoalts “I’ve discovered a waterfall and now I’m about to go straight over it,” Mr. Shoalts thought. “This is not good.” He tried to back paddle, but the current was too swift. And then, “It’s past the point of no return.” The current pivoted his canoe sideways, sending him down the 12-metre waterfall. As he...