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DULAC, La. -- On the pristine beaches of Mississippi, thousands of dead fish, stingrays, crabs and shrimp have washed ashore this month. They died from a lack of oxygen in the coastal waters of the Gulf of Mexico.

It's called the dead zone, and it appears every summer. This year's dead zone, though, is larger than average and more than twice the size of last year's.

The alarming news is that it continues to be large year after year after year, says marine biologist Nancy Rabalais has measured the dead zone since 1985.

The primary cause of the dead zone is nitrogen-based fertilizers in Midwest fields that are washed down the Mississippi River by spring rains and in to the Gulf. There they create blooms of algae that rob the water of oxygen.

In Dulac, La., David Chauvin worries about what that could do to his shrimp business.

Shrimp are one of the most fragile creatures on the face of the earth, he says. You take a shrimp and put them into a bucket with no oxygen whatsoever, they'll die within seconds. ... That could mimic a dead zone.

Click here to read more and watch the report at CBSNews.com.

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