That includes this spring's offerings. A Dutch engineering student, Boyan Slat, envisions a contraption with massive booms that would sweep debris into a huge funnel. Songwriter and music producer Pharrell Williams wants to fund the monumental cost of any cleanup by turning recycled ocean plastic into yarn and then clothes.

The challenge is huge. For one thing, the garbage is spread over millions of square miles. For another, it's made up mostly of degraded plastic, broken down by sunlight and waves into tiny bits the size of grains of rice.

"That's what makes it so horrifying," Haymet says. "The micro-plastic is the same size as the stuff living in the water column. How would we ever go out and