The annual ""dead zone"" in the Gulf of Mexico is caused by excess fertilizer running off farm fields in states along the Mississippi watershed.

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The annual "dead zone" in the Gulf of Mexico, where oxygen levels are too low to support marine life, is primarily caused by excess nutrients (particularly nitrogen and phosphorus) from agricultural and urban runoff in states along the Mississippi River watershed. Fertilizer is a major source of these nutrients.

The Annual ""Dead Zone"" in the Gulf of Mexico Is