"Dead zone" is a great exaggeration for a temporary region of hypoxic bottom water.
It's nothing but a liberal power play to exert a lot more government control over agriculture. Rather than restricting fertilizers with bigger government, a more effective approach would be to stop propping up ethanol with government mandates and let the free market reduce fertilizer usage.
There is compelling evidence that Gulf productivity is actually greatly enhanced by nutrient loading:
https://arxiv.org/ftp/arxiv/papers/1306/1306.5114.pdf
Do Louisiana fishermen really want to give up all the real, proven benefits of nutrient loading for the hypothetical negatives of temporary bottom water hypoxia?
There is also positive proof that the doomsaying predictions are exaggerated:
https://arxiv.org/ftp/arxiv/papers/1307/1307.8064.pdf
Further, there is positive proof government agencies are supporting their exaggerated claims with misleading information:
https://arxiv.org/ftp/arxiv/papers/1306/1306.5366.pdf
The Gulf of Mexico is alive and well. Cherry picking small volumes where hypoxia is present for a couple weeks some summers should not convince any thinking person otherwise.