[thackney]

IIRC, the spill is not directly in that dead zone. It would not have affected fishing so greatly if it was.

I believe that dead zone from fertilizer moves around.

Also, in the dead zone it would slow down the breakdown of oil due to the lack of oxygen.

[wolfcreek]

Dead Zone in Gulf largest since 1985.

http://www.scientificamerican.com/article.cfm?id=gulf-of-mexico-dead-zone-oil