The Dead Zone
First reported in the 1930s, the "dead zone" is an area of little to no oxygen that forms when nutrient-fueled algae blooms die.
Because the bacteria that help dead algae blooms decompose suck up oxygen from the surrounding water, an algae bloom's decomposition tends to create hypoxic or anoxic conditions: areas of water with little or no dissolved oxygen. These conditions suffocate marine life and shrink the habitat available to fish, crabs and other critters.
The dead zone is most pronounced in the deep waters of the Bay's mainstem during warm summer months. Between 1985 and 2010, the duration of the dead zone fell from five months to four, suggesting efforts to manage nutrient pollution—through upgrades to wastewater treatment plants, cuts to vehicle and power plant emissions, and reductions in runoff from farmland—are working. While rainfall and weather patterns affect the development of the dead zone, nutrient pollution is the foremost factor in its growth. The 2016 dead zone was smaller than average because of low river flow and reduced springtime nutrient-rich runoff.