The Dead Zone
The "dead zone" is an area of little to no oxygen that forms when excess nutrients enter the water through polluted runoff and feed naturally occurring algae. This drives the growth of algae blooms, which eventually die and decompose, removing oxygen from the surrounding waters faster than it can be replenished in the process. This creates hypoxic—or low oxygen—conditions that can suffocate marine life and shrink the habitat available to fish, crabs and other critters. Plant and animal life are often unable to survive in this environment, which is why the area is referred to as a dead zone. The dead zone is most pronounced in the deep waters of the Bay's mainstem during warm summer months.
In the annual Dead Zone Report Card, the Virginia Institute of Marine Science (VIMS) announced that the 2019 Chesapeake Bay dead zone covered an average of 1.5 cubic miles during the summer and reached a maximum size of 3.1 cubic miles, compared with an average of 1.2 cubic miles and a maximum of 2.5 cubic miles in 2018. To put that into perspective, at its largest, the size of the dead zone was equal to approximately 5.2 million Olympic-sized swimming pools. Overall, the 2019 dead zone lasted for 136 days—13 days longer than 2018.
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.