For the hundreds of thousands of people in the Gulf of Mexico who depend on commercial and sport fishing (directly and indirectly), the assault on sea life from the BP oil disaster has been a serious blow. But it’s hardly unfamiliar.

That’s because even before the spill, up to 8,000 square miles of Gulf waters would turn every year into Dead Zones — vast areas of the coast so depleted of oxygen that shrimp, crabs and other marine animals could no longer live.

Now, scientists fear the BP spill will make a bad situation worse. Despite blithe predictions that the Gulf fishing industry will bounce back like Alaska’s after the Exxon Valdez disaster, the already-expanding Gulf Dead Zone presents a uniquely dangerous scenario that many fear poses a long-term threat to ocean life.

First noted by scientists in the 1960s, Dead Zones are formed when huge amounts of nutrients — as found in agricultural fertilizers, municipal sewage and other wastes — overload the water, leading to explosive algae growth that ultimately robs oxygen from marine life below, a process known as hypoxia.