High tide, and the remains of a late summer storm, and it is hard to tell on this strip of land between the Mississippi and the marsh where land ends and water begins. It was here – in the most southerly reaches of Louisiana on terrain that is slowly sliding into the sea – that oil from BP's Macondo well first started coming ashore, about a week after the 20 April explosion on the Deepwater Horizon. Eleven men were killed when the drilling platform blew up.

And it is here where local people will take the most convincing that the worst of the oil spill is behind them and that recovery is under way.

Barack Obama's point man on the spill, the US Coast Guard's former commander, Thad Allen, said at the weekend that the well no longer posed any threat to the Gulf. Crews will begin the last few remaining operations needed to abandon the well this week.

People here live and die by the water. On a fine day the docks in Venice empty out, with seaworthy boats and able-bodied crew off to look for oil contamination, at sea and in the marsh grass.

No one, it seems, believes the assurances from the White House or government scientists that the oil is largely gone. And no one really believes BP when oil company executives say they will stay in Louisiana for the long haul.

They have seen one exodus already, just before Tropical Storm Bonnie blew through, about a week after the well was capped in mid-July. BP evacuated work crews and boats; many have not returned.

"Oh, the oil's out there," said a captain of one of the air boats chewing through the marsh. When the water is clear the oil pops out like a giant black teardrop. He said the air boats were carrying away up to 3,000 white plastic trash bags of oiled sand from a nearby section of marsh each day. "We'll be here for at least a year – if they still want us, that is."

The autumn shrimping season opened on schedule on 16 August and the authorities have steadily been opening up more of the Gulf for fishing. About 83% of US waters in the Gulf are now open for fishing. The first tests on shrimp, swordfish and tuna hauled out of the Gulf showed no traces of oil.

But Acy Cooper, who wears a shrimpers' white rubber boots even on days when he is not fishing, is possessed by a powerful sense of dread. How can we know for sure that the shrimp is safe from crude or its toxic components? He has seen oil in certain shrimping areas.

"We are only going to get one shot at this. If we don't do it right, we are going to be in big trouble if any tainted shrimp gets on the market," he said. "We don't want to get anything on the market that is going to kill us in the long run."

Not even the most stringent testing can ensure that fishermen stay out of oiled waters – not when some fishermen have been out of work since late April. "Some people are so hungry they are going to do what they can to survive," Cooper said.

Already the local economy is being transformed. On noticeboards, cards for mental health services and lawyers offering to sue BP are tacked on top of advertisements for fishing guides. It is getting harder to find a market for fish.

The other day George Barisich, the head of the United Commercial Fishermen's Alliance, had to drive all the way into Mississippi before he could find a processor who wanted his shrimp. He said he was reduced to selling for just $1.40 (90p) per pound.

Officials from the National Oceanic and Atmospheric Agency have been on local radio shows, such as Talk of the Bayou, trying to persuade fishermen like Cooper they have nothing to fear.

"So far we haven't seen a bit of evidence the oil is getting real deep in the marsh," said Jacqueline Michel, a NOAA biochemist.

Only 22 of the 2,000 water samples taken from the Gulf contained traces of oil, and none has permeated deep into the wetlands, which are breeding grounds for shrimp.

The callers were not buying it, and neither was Cooper. He worries that the last few months may have ruined the fisherman's life for some.

Although local people complain that BP gave too many jobs to outsiders rather than locals for cleanup work, some taken on have become used to earning good money – even when they were waiting around at the marina – on the oil company's "vessels of opportunity" programme for the cleanup.

Cooper is worried they may give up on shrimping, now that it's such an uncertain occupation.

"We are on the verge of losing this industry," he said. "The chain is broken with the vessels of opportunity."

For Al Sunseri that chain stretches back to 1876 when his family set up the P&J Oyster Company on the edges of New Orleans' French quarter.

He still turns up for work at 4.30am, but there are no workers shucking oysters on the loading dock. Eleven people have been let go.

Premium oysters are a vanishing commodity. Those oysters not killed by the oil were finished off by the Louisiana government's decision to flood the Gulf with fresh water to try to keep the oil offshore.

Sunseri now occupies his time taking orders on a clipboard, trying to mollify the desperate chefs who are his main customer base. He is running dangerously low on shucked oysters.

He asks callers if they could get by with a smaller order. "I am just going to have to tell people I don't have them and that is not something that I am used to doing," he said.

The shortage has pushed the price of oysters in the shell up 40% since the spill. That is too rich in the depths of a recession – even for a luxury product. Sunseri also worries that what oysters he can find are of variable quality.

"I know they say about 40% of the oyster growing area is open but as far as productive areas, it is maybe about 15%," he said. "We don't have babies, and we don't have the market-sized ones."

He moves over to a tabletop display of oyster shells. Those that are being harvested are about half normal size. "These would ordinarily not be harvested for another year," he said.

"They really should be in there developing. The few little oysters that I am selling right now are really inferior."

Even industry cheerleader Mike Voisin, who chairs the Louisiana Oyster Task Force, admits it will be three years before the oyster beds resettle. Until then, he says, the harvest will probably fall to half of the usual 113,000 tonne annual take.

The timespan is depressing for Sunseri. He said he is telling his children: "Your daddy does not care if this business fizzles away. Don't feel the burden of carrying this on."

For Ryan Lambert, who once counted himself the biggest fishing charter operator around Venice, such acceptance is unthinkable. He is much too angry to be resigned.

The spill left him with a calendar showing week after week of cancelled bookings, gutting a business that once brought in $1.3m a year.

By BP's reckoning though, his losses were just $66,000. Lambert is furious. He said he has paid his accountant hundreds of dollars to meet BP's demands for documentation. "I shouldn't have to fight for the money that is owed me," he said. "I am not the bad guy here. They are the ones who ruined it for me, not vice versa. For me to have to fight for them to pay me for what they did makes me sick."

He is also worried sick that the fish will start disappearing, as they did in the years after the Exxon Valdez spill in Alaska, and that his business will be dealt a slow, painful death.

He built his company from scratch, starting from his love of bass fishing; now his clients troop into his fishing lodge from all across the country. He rebuilt once before, after Hurricane Katrina. He is not sure he can do it again, or wait for the Gulf to make a full recovery.

"I am 52 years old. I can't wait 20 years for them to clean things up."

He feels certain BP will pull out much sooner. "The well will be stopped, and then they will hang around until the oil stops coming up on the beaches, and then they will be gone," he said.

"Anything they don't clean will be left to me and the microbes and Mother Nature until all of a sudden we won't be America's best fishery any more.

"This will be history some day, and I will still have that problem."

Sept. 6, 2010

www.guardian.co.uk/environment/2010/sep/06/bp-oil-spill-fishing-fears