Why the Gulf of Mexico dead zone forms every year

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Every year, an ominous phenomenon occurs in the Gulf of Mexico.

It’s called a dead zone.

Every summer, this 5,000-square-mile (on average) region becomes nearly devoid of oxygen, meaning marine life can’t survive.


Counter-intuitively, the dead zone forms because of too many nutrients in the water.


Fertilizers packed with nutrients like phosphorus and nitrogen leach out of farm lands along the Mississippi River and head downstream.


Once they deposit into the Gulf, they become food for algae. Growth accelerates and algae takes over.


When that algae dies and sinks to the ocean’s bottom, bacteria start to decompose it.

That decomposition process sucks oxygen out of the water, leaving very little for fish and other marine creatures to survive.

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Some creatures can swim away. Others, like crabs or shrimp, can’t escape the oxygen-poor waters.

Researchers say that reducing fertilizer use and stopping animal waste from reaching waterways are possible ways to decrease the size of the dead zone.

Read a deeper-dive dead zone explainer here.