Every spring, as the snows thaw, water rushes down the Mississippi and Missouri rivers, spreading life, then death into the Gulf of Mexico. The floodwaters are laden with fertilisers washed from fields and factory farms. As spring turns to summer, excessive nutrients first drive a huge bloom of living plankton, then cause death on a gargantuan scale as a dead zone blossoms across the seabed. Most years it grows swiftly to over 5,000 square miles of seabed, killing everything that cannot outrun it.

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This year’s dead zone has engulfed 8,700 square miles, the biggest ever recorded.

A new report lands much of the blame for the dead zone at the door of modern industrial agriculture. America’s addiction to cheap meat, fed on corn and soy in vast indoor factories, comes at a high cost in human health problems and environmental destruction. None of these costs are paid for by the companies that produce the meat and feed, such as Tyson, Cargill and ADM.

Agriculture was very different before the second world war, when animals were mostly kept outdoors. Cows grazed on pasture and rangeland, while chickens and hogs rooted over fields, supplemented with food and crop waste. Chemicals were little used.

In the last few decades, meat production has intensified and become big business for the agrochemical industry. Animals have been moved indoors into crowded feedlots where they are fattened on corn and soybeans grown, ironically, on the rangeland the animals vacated. Cropland is eating into the remaining prairie, making this wildflower rich habitat one of the most endangered in the US.

Crops grown to supply meat production consume vast quantities of fertilisers, herbicides, fungicides and pesticides, much of which wash into streams and rivers, and then downstream to the sea. Indoor animals are pumped full of veterinary drugs to counter the disease risks of high-density living. The drugs find their way into watercourses from urine, manure and abattoir waste.

Plankton, the microscopic plants and animals that drift in the open sea, fuel ocean food webs. Normally, they are limited by lack of nutrients, particularly nitrogen and phosphorus, the key ingredients of farm fertiliser. But in certain parts of the sea, nutrients, light and warmth come together in just the right quantities.

One such area was the “fertile crescent”, an area west of the Mississippi Delta, once famed for its abundant marine life and prolific fisheries for fish and shrimp. But agricultural pollution has destroyed it.

The Mississippi drains 40% of the lower 48 states, including much of the midwest agricultural belt. Corn and soybeans for industrial meat production produce half the nitrogen and a quarter of the phosphorus pollution reaching the Gulf of Mexico. So much fertiliser washes into the Gulf today that the planktonic explosion of life is excessive. Come summer, the short-lived plankton die and sink and their rotting bodies suck up all the oxygen dissolved in the water. The deathly shroud kills indiscriminately.

There are more than 550 dead zones across the world today, the great majority due to agricultural and industrial pollution. Meat consumption is growing fast, encouraged by low prices that do not reflect the true costs.

As Philip Lymbery argues in his compelling book, Dead Zone: Where the Wild Things Were, if the costs of pollution, habitat destruction, losses to fisheries and tourism, climate change and impacts on human health were fully accounted for, meat would be a luxury food.

Industrial agriculture and our diets must change if the world is to prosper. By eating more vegetables and less meat, reared outdoors in humane and sustainable ways, we would all be better off.