Scientists are predicting this year’s Gulf of Mexico dead zone will be the largest ever.

In January of 2008, USGS identified commercial fertilizers and animal manure from farmland in 9 states as the cause of over 70 percent of the Dead Zone pollution. Evidence is mounting that the mandated push to increase corn production – one of the most fertilizer intensive crops – for ethanol exacerbates water quality problems within the states and in the Gulf.

The 9 states contributing over 70 percent of the dead zone-causing nitrogen and phosphorus pollutants are: Illinois, Iowa, Indiana, Missouri, Arkansas, Kentucky, Tennessee, Ohio, and Mississippi.

In April of 2009, the U.S. Geological Survey identified 42 Iowa watersheds as among the top 150 watersheds contributing too much nitrogen and/or phosphorus to the Gulf of Mexico and the resulting Dead Zone.

More details at this science blog by Eric Berger with good link to an explanation of the Dead Zone.