The dead zone in the Gulf of Mexico is 5,052 square miles is smaller than it was last year, researchers with NOAA and the EPA announced this week. But it's still very, very large—about the size of Connecticut and much bigger than 1,900 square miles that the Mississippi River/Gulf of Mexico Watershed Nutrient Task Force has set as a target.
The dead zone is also one of the largest in the world, second only to the dead zone in the Baltic Sea.
Every year, 1.7 million tons of nutrients travel to the Gulf of Mexico from fertilizer on farms and other runoff that flows into the Mississippi. This great video by NOAA illustrates how these nutrients can lead to dead zones, by providing an all-you-can eat buffet for phytoplankton, creating huge blooms.
Eventually, the phytoplankton die or are consumed by other creatures. Decomposition bacteria get to work, breaking down the waste and the phytoplankton’s microscopic remains. As they eat, the bacteria use up oxygen in the water, creating a huge area with low oxygen—the "dead zone." Without oxygen, marine creatures have to either move to other areas of the ocean, or die.
As we saw in Toledo earlier this week, algae blooms can be harmful to humans too, especially when they produce toxins and are unfortunately situated near water intake stations.