Moore began that voyage in 1997 as a simple sailor, not yet the ardent activist he would become. He completed a trans-Pacific race and then changed course to hightail it back to the Mainland; to get there faster, he ran on engines through a rarely traversed section of the North Pacific, the Central Gyre. (A gyre is a “converge zone,” a place with little wind and current where debris tends to amass.) There, Moore made his discovery: a massive sea of plastic floating in the North Pacific. “As I gazed from the deck at the surface of what ought to have been a pristine ocean,” he remembers, “I was always confronted with the sight of plastic. 

It seemed unbelievable, but I never found a clear spot. In the week it took to cross the subtropical high, no matter what time of day I looked, plastic debris was floating everywhere: bottles, bottle caps, wrappers, fragments.”

Shocked, Moore returned two years later on the first of his research expeditions to determine the scale and significance of the plastic garbage patch he’d stumbled on. It was, he extrapolated from samples he took on that first trip, bigger than Texas, a synthetic soup in which plastic particles outnumbered plankton by a stunning six-to-one ratio. Moore returned to California and started doing everything he could think of to warn the world: focusing his Algalita Marine Research Foundation on the issue, giving talks, consulting with any organizations or government agencies willing to listen. But it was slow going on a planet already coping with global warming, overfishing, coral bleaching and more.

Nine years later, in 2008, Moore embarked on his sixth research trip to the North Pacific. By then things had grown much, much worse. The garbage patch had swelled to cover the entire North Pacific Subtropical Gyre, an area roughly twice the size of the continental United States, and its ratio of plastic to plankton had grown to an astounding forty-six to one. In some places, Moore found more than a million tiny pieces of plastic per square kilometer. The inescapable truth, as he would put it succinctly: “We’ve changed the fundamental character of ocean water. Plastic is now a new component.”

Three assistants joined Moore on the sixth trip: Marcus Eriksen, Joel Paschal and Anna Cummins. Out in the gyre, in the middle of a mess that extended to the horizon in every direction, they racked their brains about how to help stanch the flow of plastic in and get the word out. The answer they came up with was more than a little gonzo: They would build a raft out of thousands of plastic bottles and sail it from California to Hawai‘i. It would be activism joined with adventure—and ultimately, they hoped, the world would be better for it.