Marshland is country that is marsh — low, wet, and soft underfoot, often stretching a long way. We use it when we are thinking of a whole area, not one small wet patch by a path. Farmers may drain marshland to grow things; birds still need what is left. It is a quiet, ordinary word. Marshland, a marsh, and a marshy field sit very close in meaning, and people do not always keep them apart. Though actually, marshland puts the stress on the land as a stretch of country, the kind you might see from a train window, all reeds and water and sky.