Those who live in Louisiana all their lives develop an understanding of disaster. We know a hurricane can turn over hundreds of offshore oil rigs in one pass and then come to land and do the same to our homes. Refineries explode, rigs blow up, pipelines burst, well pressures cause accidents that take fingers, feet, arms, legs and life itself.

There's hardly a family in the Gulf region that does not have a member involved in the oil industry. My father was a tugboat captain who handled barges of crude oil for the sprawling refineries, my brother sells oilfield equipment and technology, my nephew captains offshore supply vessels, my great-nephew operates a giant crane currently picking Katrina-smashed equipment from the Gulf floor. Cousins manage oil leases.

So, even though I am not an oil worker, the industry is part of my environment, my history, and when I saw images of the April Deepwater Horizon explosion and fire, I thought at once, "Wait a minute. Something's wrong. That rig is state-of-the-art, the size of a small factory, loaded with technology that rivals the space programme in complexity. Why is the fire so enormous?" And later, when the labyrinth of pipes and valves keeled over in a rumbling, hissing nimbus of flame, I was astounded, thinking, "Why didn't the blowout preventer shut down the well?" And days later, when it was revealed that the device was not functioning, a dark spill began to spread in my soul, a burgeoning realisation that nothing could stop a runaway well 5,000ft below the Gulf's surface. Nothing. A wide open fire hydrant blasting a plume of water out of a four-inch opening operates on a pressure of 50 pounds per square inch. The oil and gas venting from the rig's seven-inch pipe is propelled by at least 3,000 psi. Or more. And if the pipe beneath the blowout preventer fails? The reservoir pressures, I understand, are 11,000 psi. Unchecked, the subterranean caverns of oil would roar to the surface for years. BP has made a number of attempts to stop the fountain of oil and all have failed, except for the latest cap. But even this success poses many dangers, including a well rupture far below the ocean floor, initiated by the high pressure caused by the cap. No one knows what the result of such a failure would be, and this highlights the most frightening facet of the catastrophe: its unpredictability. The final solution is supposed to be the relief wells BP is drilling, and on the day I realised even these might not arrest the blowout, I decided to stop thinking about it all.

I drove into my south-east Louisiana town of Hammond to get something good to eat. At a seafood cafe I ordered Oysters Scampi. The TV was on above the bar, showing miles-long strands of red oil streaming across the face of the Gulf. I thought of the men killed in the explosion, how they spent their lives trying to avoid something like this. My oysters were large and plump; I ate the first fellow, then looked up at the oil. Locally, it's well known that 60% of the US's oysters come from Louisiana's coastal regions. The oyster beds would be killed by the oil and take years to regenerate. Longer, if the oil kept coming next year. And the next. The spill inside me widened as I realised that the shrimp fisheries would soon be closed, the commercial taking of red snapper, grouper and all their delectable cousins banned. I remembered that Louisiana supplies 73% of the nation's shrimp. My God, what about the charter boat industry and sport fishermen from Texas to Florida?

The nightly news told of oil coming ashore. Unlike its neighbour states, Louisiana has no shore, no sand beach except for a small spit called Grand Isle, no dunes, hills, cliffs. The entire Gulf border and its wide attendant marshes are exactly at sea level. The shore is mostly gritty mud held in place by tall, dense marsh grass. What is not water is grass, thousands of square miles of it. When the oil kills the grass, the shore will begin to melt away. This coastal marsh is home to millions of birds – pelicans, terns, egrets, great herons – and a rich variety of mammals and reptiles. It is threaded through by countless miles of narrow bayous, inlets and lagoons, all spawning areas for shrimp and succulent blue-claw crabs, nesting grounds for vast flocks of migratory geese and ducks – a hot and humid greenhouse teeming with life.

Louisiana is a relatively small state, but it contains 40-45% of the nation's coastal wetlands. The neighbour states of Texas, Alabama, Mississippi and Florida have similar fertile and productive marshes, though such areas are much smaller.

The oil that began to show up, the so-called tar balls, were really reddish pancakes of axle grease; they began to appear on Grand Isle, then east, on the Alabama beaches, followed by a nasty invasion of the lovely green water and white sand shores of Pensacola and Santa Rosa Island. Heavy dark oil began to pool against the Louisiana marshes, coating wildlife with a greasy, glue-like batter – no one can ever know how many thousands of animals have died, how many carcasses are at the bottom of the quarter million square miles of the Gulf.

Next, every fisherman's greatest fear happened. The government had to close over 80,000 square miles of the Gulf to all fishing, and suddenly tens of thousands of fishermen were out of work, losing their identity and a way of life they and their ancestors have pursued for generations. The Cajuns have fished since they arrived in the 1700s; the Vietnamese, Croatians, African Americans, Native Americans, Islenos and plain American country boys who trawl and fish and process are all on the bank watching their livelihoods drown in oil. How much oil? Who will ever know? As of now, a safe final estimate, if the cap holds and the relief wells work, is 200m gallons. The oil washing up in July might have leaked in April. Locals are losing sleep about how much oil is looming underwater to bedevil us next year or for 10 years. Calls to counselling and crisis lines are through the roof. Fourteen million people depend on fishing and oilfield work for a living in the Gulf region. The fishermen can't pay rents and mortgages, utility bills, insurance, buy fuel for their boats, save for any kind of future; they stand in charity food lines on 100-degree days. The oilfield people are facing cutbacks because of the new ban on deepwater drilling; this is affecting shipbuilding, crewboat, supply and helicopter fleets, machine shops, pipe yards, supply houses, foundries and a hundred other businesses. The fishermen are hurting acutely at the moment, but the oil workers are worried for their futures as well, as the industry is facing a wind-down that could last for years. The news keeps getting more uncertain and, yes, things can get worse because hurricane season is now upon us and no one knows what havoc a big storm in the Gulf could cause. It could do anything from pushing a bow wave of killing oil over the estuaries to painting New Orleans with black rain.

I don't think people living outside the region understand what is happening. One so-called environmentalist suggested Gulf fishermen and oil workers should just get educated in green technology and work in solar panel factories. What are they supposed to do for 20 years until the technology is perfected and the factories built? Fishermen want to work as fishermen; the Gulf is 1,000 miles wide and they are independent members of a huge culture, not employees.

By the end of June I tried to limit my news intake. It was now clear the enormous Gulf tourism industry was on shaky ground because all the beaches from Panama City, Florida to Grand Isle, Louisiana were fouled or soon to be fouled, and the result was a freefall in hotel, condo and restaurant bookings, and trade in the thousands of gift shops, filling stations, convenience stores, bait-and-tackle shops… Each type of business was firing workers, cutting orders, falling into debt.

After a charter boat captain shot himself in the head, I turned off the television. But everywhere I went, neighbours, bank tellers, waitresses, university professors all fretted about the spill. Last year, one billion pounds of fish was harvested from the Gulf; now only a tiny fraction of that is being caught in the small areas still open, and chances are even that clean catch will be distrusted by buyers outside the region. How many years will it take for Gulf seafood's reputation for quality to return?

This disaster rides like a tumour on the back of the monster Katrina, a storm that in 2005 killed more than 1,800 people in the New Orleans area. Many residents of the region were finally getting their homes rebuilt, their boats and docks restored.

It is true a few hundred men have been hired by BP at low wages to shovel muck off the shores. Several motels have been rented to house workers and BP has been leaking out cheques to fishing families and charter boat operators (though there are tales of cheques never arriving). Hundreds of boats have been hired to go after the oil, but not a man in a thousand miles is glad about any of it.

Everyone has a sense of why the accident happened. Weeks before the explosion, it seems BP knew the blowout preventer was leaking and missing a crucial seal. About 10 hours before 11 men were burned up, employees report an argument broke out between the rig's BP manager, who wanted a speedy and cheap sealing of the well, and the driller and cementer, who demanded traditional, safe plugging methods. The company man overruled the experts. He wanted to save money, ignoring the first rule of industry economics: safety is never more expensive than an accident.

The clean-up bill is complex and will extend for years. In Florida, workers clean a beach at dusk; at sunrise it's covered again. The spill is slathering four states now. It could be blown over to Texas. It could show up in the marinas of Key West, or even Wilmington, North Carolina on the Atlantic, wherever the Gulf Stream carries it. The coming expense is not to be imagined. Lawsuits are spilling out with no judicial blowout preventer to slow them down. Injury and loss of livelihood suits, suits from hotels for loss of bookings, suits from restaurants, bars, stores, suits for mental anguish, even claims from municipalities for loss of taxes.

The future? There is a large, years-old black spot in my driveway where my old Jeep once leaked a quart of transmission oil. It's not fading away. The BP spill is likewise staining the coast's soil, and sinking into the psychological fabric of the Gulf. Beneath the sorrow lies suspicion and anger based on the notion that if this spill had occurred near a place like Boston harbour where a lot of wealthy, well-connected people live, every oil-skimmer in the hemisphere would have been brought in and every offer of foreign help accepted immediately, instead of 71 days after the spill began.

The locals have watched with disbelief some of BP's lunatic and expensive clean-up methods, such as wiping down each blade of marsh grass with paper towels. They have watched their own, more effective, home-grown efforts ridiculed and crushed by irrelevant Coast Guard regulations and "experts" who have never seen Louisiana's coast except perhaps through the windows of a plane.

In three to 10 years, maybe the lawsuits will be settled, maybe the sea grasses will grow back to hold the marshlands together, maybe the fish now trying to breathe clouds of undersea oil will somehow propagate, maybe trust in the world's best seafood will return. But a person's life is composed of minutes and is most fulfilled by working and bringing one's earnings to the family table. And who can give back even one ruined minute?

• Click on the link above to see an extended slideshow of Stuart Franklin's photographs.