The largest ocean dead zone in the world, currently, is in the Gulf of Mexico near the Louisiana/Texas shelf and stretches all the way to the Mississippi River. It is 200 feet deep and in 2007, was approximately 7,900 square miles. This is almost the size of New Jersey. The dead zone is a seasonal occurrence triggered by the high nutrients in freshwater coming down from Mississippi from melting snow and spring rains. They typically form in May and remain until September or October. This dead zone is in one of the most productive fisheries areas in the United States and there is great concern that shellfish is being affected and will be affected if hypoxic conditions continue or worsen.
Only a few of ocean dead zones have recovered from low oxygen levels. The Black Sea rebounded quickly in the 1990’s when the Soviet Union collapsed. There were massive reductions in fertilizer runoff from fields in Russia and Ukraine. These fertilizers contained large amounts of Nitrogen from agriculture, but with the fall of the Soviet Union a lot of farming practices ended.