It is an anxious summer for watermen harvesting the Chesapeake Bay’s best-loved seafood, the blue crab. Crabs have thrived in the bottom muck of the Chesapeake and its tributaries even as centuries of overfishing harmed oysters, fish and other species in the nation’s largest estuary. Now blue crabs are in trouble. Virginia and Maryland fisheries managers say the bay’s blue crab stock is down 70-percent since 1990 due to overfishing and water pollution. The states have imposed steep cuts on this year’s female crab harvest, aiming to reduce the number of crabs taken by more than a third. Even scientists who called for the harvest reductions say overfishing is not entirely to blame. The main culprit is water pollution and soil runoff from development throughout a watershed that is home to 10-million people.