At the southern edge of Louisiana, the Mississippi River drains into the Gulf of Mexico and brings death. Fish and other sea life cannot survive in this area. Spreading 7000 square miles from the foot of the Mississippi River is an area known as the Dead Zone, or Hypoxic Zone.
Hypoxia is when water has little to no dissolved oxygen in it.
Many marine creatures breathe oxygen, just like you and I do. Low oxygen levels generally begin in the spring, due to high nutrient levels in the Mississippi and its tributaries. Many row crops like corn, and soybeans, need nutrients like nitrogen to grow. But, when the spring rains come, those same nutrients wash off the fields, and run right into the rivers. The huge amount of nutrients in the rivers are eaten by phytoplankton, a tiny aquatic plant.