. >> the chesapeake bay, the nation's largest estuary, are over the years daife dave kerwin has seen the bay overwhelmed by a combination of fing agricultural runoff. >> used to be grass, when i was a kid grass would be all the way across it back in the '60s. when they started using fertilizer, started stepping out of agriculture and the runoff that's what killed you all the grasses. >> will baker of the environmental group chesapeake bay foundation says the same. >> we are talking about fin fish, shellfish, wetlands, the water clarity, the dissolved oxygen in the water, the way the bay supports recreation, tourism even property values. so the system is degraded. it's a system dangerously out of balance. >> the polluted waters of the chesapeake bay are polluting more than the fish. they are also changing local fishing communities, rock hall, on maryland's eastern shore. >> rock haul is changing from a acquaint fishing villages, all the businesses used to revolve around the water business. when the water is in the decline the other business is in the decline. >> since 1972 the clean w