Researchers on an expedition to assess the state of plastic pollution in the North Pacific Ocean discovered two disturbing things: an island completely made of trash, large and sturdy enough to walk on; and a piece of radioactive rope floating in the midst of the ocean.

The "garbage island" was discovered by researchers from the nonprofit Algalita, which studies plastic pollution, about a thousand miles to the west of California, and about a thousand miles north of Hawaii. It is located in what is known as a gyre, where ocean currents meet and circle. Because of the nature of these currents, garbage tends to accumulate in gyres. It was in just such a gyre that, 15 years ago, Algalita researchers discovered the giant plastic mass that has come to be known the "Great Pacific Garbage Patch."