The flow of farming chemicals such as nitrogen and phosphorous fertilizer has created a dead zone in the Gulf of Mexico flowing out of the Mississippi River that would take 30 years to heal even under the most impossibly rosy circumstances. Unfortunately, this hugely oxygen-deprived dead zone continues to grow due to the unsustainable applications by intensive agriculture that is also depleting fertile soils. This area is a small piece of the global suffocation of the oceans and fresh surface water bodies and rivers caused by modern agriculture, and in addition to the effects of improperly managed sewage and climate change, are putting in peril water resources and aquatic ecology globally.
https://www.theguardian.com/environment/2018/mar/22/dead-zone-gulf-of-mexico-decades-recover-study
