How A Once-Toxic Cape Cod Lagoon Became A Horseshoe Crab Haven NORTH TRURO, Massachusetts — It’s a warm, sunny June morning as Sophia Fox pulls on her wetsuit and wades into the cool waters of East Harbor. About ten feet from the shore, she stops, scans the surface, and plunges her arm into the shallow waters. Waves ripple outward, and for a moment, nothing happens. When she straightens again, her cupped hand lifts something out of the water, dripping into the light.