The largest 'dead zone' ever recorded is headed for the Gulf of Mexico this summer, as high levels of pollution runoff, elevated by Midwestern floods, seep into the ocean.

The dead area could grow to as much as 8,500 square miles of toxic deep ocean water—killing all marine life in its path—warn National Oceanographic and Atmospheric Administration scientists.

The findings signal a warning not only about the Gulf of Mexico, but about the many dead zones that develop each year across the world's oceans.

Dead zones emerge deep beneath the marine surface when pollution runoff from farms seeps into the ocean, releasing nitrogen that feeds large algae growths.

When areas become over-grown with algae because of excess nitrogen, they become depleted of oxygen and thus toxic to marine life, choking and killing fish in a process scientists call 'hypoxia.'

"Dead zones are becoming more common worldwide in areas where coastal waters are swamped with nutrients, particularly nitrogen, from sewage or fertilizer," NOAA scientists explain.

This year's runoff is especially bad, because heavy rains and floods this spring are flushing Midwestern farm pollutants into the ocean.

The Gulf of Mexico dead zone is expected to swell far beyond its usual 18,000 kilometers, alarming scientists.

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Unregulated large-scale farming is to blame for the vast pollutants the rain washes into the ocean. Time Magazine reports:

The major factor driving the size of the dead zone—beyond changing flooding patterns—is the use and overuse of fertilizers in America’s rich Midwestern corn belt. The U.S. Geological Survey estimated that 153,000 metric tons of nutrients flowed down the swollen Mississippi and Atchafalaya rivers during May—a 16% increase over the nutrient load average seen during the past 34 years.

As Bloomberg points out, ethanol production carries much of the blame:

The culprits behind the dead zone are many, but one deserves special attention: corn. Unlike, say, soybeans, which can grow without fertilizer, corn can't grow without it. It takes 195 pounds of fertilizer to grow an acre of corn. And the U.S. grows a lot of corn -- more than any other country. What's more, 40 percent of the U.S. corn crop is devoted to making ethanol, which fuel companies must blend with gasoline under a congressional mandate. The Gulf dead zone is yet another reason for Congress to kill that mandate.

Green groups charge that the lack of state and federal regulations of big agribusiness is responsible for the toxic zones choking ocean life. State and federal initiatives are too reliant on farmers' voluntary self-regulation and come nowhere near to meeting nitrogen reduction goals.

In May, native and indigenous communities walked over 1,700 miles along the Mississippi calling for an immediate halt to the flow of pollutants into the river.

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