https://www.theguardian.com/commentisfree/2017/aug/04/meat-industry-gulf-mexico-dead-zones-pollution
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.
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.
....
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.
see report at
http://www.healthygulf.org/sites/healthygulf.org/files/final_lsu_lumcon_2017_hypoxia_forecast.pdf 
