It's called the dead zone - a 5,000-to-7,000-square-mile layer of lifeless water in the Gulf of Mexico. Every spring and summer, it steals needed oxygen from bottom waters, repelling fish and killing important organisms in the mud below the sea.
And this year, it's poised to suck environmentalists and agricultural interests into a sharp battle that could change the way the Midwest farms its land. At stake are higher food prices, millions of acres of crop land and waterfront property, a fragile coastal ecosystem, and the health of lakes and rivers throughout the 26-state Mississippi River Basin.
As farmers head to their fields for spring planting, the US Environmental Protection Agency (EPA) is creating a dead-zone action plan - one that should be in place by next year.
What the agency decides to do could determine just how far the United States will restrict farm production in order to clean up its water - not just in the Gulf but nationwide.
"Nutrient pollution is one of the most pervasive water-quality problems facing this nation," says Charles Fox, assistant administrator for water at EPA. "We owe it to future generations to work aggressively to solve this problem. And I think we can do it, but it's not going to be solved overnight."
The battleground is fertilizer. Every spring, farmers apply nitrogen to their land to boost corn production. The problem, researchers argue, is that they use too much nitrogen, and the excess gets washed into gullies and streams, moves into rivers, and eventually finds its way into the Gulf via the Mississippi River.
The problem is not all the farmers' fault. Lawn fertilizer, fertilizer production, industrial waste - even car exhaust - create excess nitrogen that's deposited on the land and causes everything from acidification of lakes and streams to the loss of soil nutrients and, probably, the decline of certain marine species.
"It has a lot of consequences," says Peter Vitousek, a biology professor at Stanford University in California. "In areas where there's a lot of nitrogen from fertilization and fossil-fuel combustion, you get significant effects on forests and fields and diversities of vegetation."
The problem is particularly spectacular where fresh-water sources dump into the oceans, creating giant algal blooms in places such as Chesapeake Bay, Long Island Sound, and, largest of all, the Baltic Sea in northern Europe.
In North America, the biggest of these algal blooms is the so-called dead zone in the Gulf. It's created because the Mississippi and Atchafalaya Rivers dump too many nutrients into the sea. Because the rivers' fresh water is less dense, it floats on top of the saltwater, forming a giant layer that stretches for thousands of miles off the coast. The algae flourishes because of the nutrients, but eventually they die or get eaten by other microscopic organisms, who discharge waste.
Either way, excess organic matter drops onto the seabed, gets decomposed by bacteria in a process that uses up the oxygen in the saltwater.
The result: a low-oxygen condition called hypoxia that forces fish and shrimp to swim away. Important marine life that can't leave can eventually die - hence the term dead zone.
ONE of the likely battles between farm groups and environmentalists will be over how damaging the dead zone actually is. A just-released study for the EPA concludes it's had little measurable commercial impact on Gulf Coast fisheries, at least so far. And the authors conclude there's too little data to assess the zone's ecological implications, although if conditions worsen, fisheries could decline, they warn.
The study is one of six scientific assessments of various aspects of the dead zone now being published for the EPA. Another assessment suggests that under the scenario with the least economic impact, farmers should cut their fertilizer use 20 percent, while state and federal governments restore 5 million acres of wetlands to soak up nitrogen in the upper Mississippi River Basin.
That scenario would cause farmers in the Mississippi River Basin to plant somewhat less corn, cotton, and other crops, which would cut the nation's exports but raise prices enough to boost farmers' income overall.
But livestock producers would have to spend more for feed, and US consumers would have to spend more on food than farmers would make. On balance, a relatively modest net cost of $4.8 billion a year.
But some agricultural economists doubt farmers will see a long-term rise in income from the reduction in crops. "Our competitors around the world would fill the gap," says Terry Francl, senior economist for the American Farm Bureau Federation in Park Ridge, Ill. And "we would lose export numbers."
Also, corn farmers typically use 25 percent less nitrogen fertilizer per acre than they did in the mid-1980s, when the dead zone was being mapped, he points out. Furthermore, some researchers argue that while the data suggest a link between nitrogen fertilizer and the dead zone in the Gulf, they don't prove it.
"It's a very complex phenomenon, which has a variety of causes," says Anne Carey, associate research engineer at the University of Alabama in Tuscaloosa and author of a soon-to-be-published study funded by the US fertilizer industry. "If we don't know what the cause is, then regulating something ... may well not solve the problem."
But a larger contingent of researchers argue that the circumstantial evidence is strong enough that policymakers should move forward.
"We can't put the Gulf of Mexico in a test tube and add nutrients," counters Nancy Rabalais, a researcher at the Louisiana Universities Marine Consortium in Cocodrie, La. But "you can deductively reason that there's a link.... There are lots of examples in other places in the world where nutrients have been reduced and water quality has been improved."