The Gulf of Mexico is in for its "largest ever amount of hypoxia." And that's not a good thing.
Natural processes used to occasionally create a "dead zone" of oxygen-poor water grows in the waters of the Gulf of Mexico. It would happen when nutrients from upstream got washed out to sea, feeding phytoplankton in the area. As that phytoplankton population exploded, and then decomposed, bacteria would absorb the water's oxygen, making it deadly to animals, from crustaceans to fish.