In the winter of 1983, the largest El Niño event on record, a series of "superstorms," battered the West. That spring, a massive snowmelt sent runoff racing down the Colorado River toward the Glen Canyon Dam. As the water filled the dam, worried federal officials desperately scrambled to avoid a dramatic dam failure. In the midst of this crisis, a trio of river guides secretly launched a small, hand-built wooden boat, a dory named the Emerald Mile, into the Colorado just below the dam's base and rocketed downstream, where the torrents of water released by the dam engineers had created a maelstrom. The river was already choked with the wreckage of commercial rafting trips: injured passengers clung to the remnants of three-ton motorboats that had been torn to pieces. The chaos had claimed its first fatality, further launches were forbidden, and rangers were conducting the largest helicopter evacuation in the history of Grand Canyon National Park. A river run under such conditions seemed to border on the suicidal, but Kenton Grua, the captain of that dory, planned to use the flood as a hydraulic slingshot that would hurl him and two companions through the most ferocious white water in North America on the fastest boat ride ever through the Grand Canyon.