Like colorful corals, they rocked gently in the ocean current. Only these were not beautiful natural reefs grown over centuries. They were plastic bags, stuck to the Aegean Sea floor since a waste site slid into the water eight years ago. A team of divers and environmentalists pulled thousands of plastic bags from the water near Greece’s Andros island this month. The workers described what they found as a “gulf full of plastic corals.” Seas polluted with plastic have become one of the most shocking signs of human damage to the planet.