My first sight of it came one morning in June, as I rode the ferry through the Bosporus strait: a toxic glint on the sea’s surface. I initially thought it was oil, spilled from one of the many large container ships that pass through Istanbul via the Bosporus. Yet as we neared the glint, a sallow sludge marbled the water around the boat. In some areas, it was as thick and buoyant as fiberglass insulation. Its surface, coated with foamy bubbles and viscous puddles, was littered with balloons, bread crusts, and Styrofoam food containers.