Annual massive “dead zone”

CNN delivers [this cheerful story](http://edition.cnn.com/2004/TECH/science/08/04/environment.deadzone.reut/index.html)  about an enormous area of the Gulf of Mexico that is so polluted that nothing at all can live in it for several months of the year.

American farmers use nitrate-based fertiliser, which gets washed down the Mississippi river and into the gulf. Nitrates rob oxygen from the water, forcing sea creatures to move or die. These fertilisers are not unique to the US – I wonder how many other “dead zones” are lurking in the ocean.

What if dolphins created massive amounts of air pollution, killing hundreds of thousands of people? I’d be plenty pissed off.