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 and decompose. Because the decomposition process removes oxygen from the water faster than it can be replaced, the decomposition of an algae bloom creates hypoxic or anoxic conditions that can can 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.
In 2017, high spring flows from the Susquehanna River led experts to predict a larger than average dead zone. While strong spring winds delayed the dead zone's onset, hypoxic conditions rose in early June and the dead zone was found to be about ten percent larger than the previous year.