The Dead Zone

When nutrient-fueled algae blooms die and decompose, the resulting low-oxygen conditions—known as “dead zones”—can suffocate underwater life and shrink available habitat.

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. 


The average size, in cubic miles, of the 2020 Chesapeake Bay dead zone

In the annual Dead Zone Report Card, the Virginia Institute of Marine Science (VIMS) announced that the 2020 Chesapeake Bay dead zone covered an average of 1.0 cubic miles during the summer and reached a maximum size of 2.7 cubic miles, smaller than most recorded in the past 35 years (80%). Overall, the 2020 dead zone lasted for 95 days—41 days shorter than 2019. In the short-term, experts believe that several factors, including more average river flows and unseasonably cool temperatures in May and September contributed to the smaller dead zone. Over the long-term, the continued implementation of nutrient and sediment reduction strategies put in place by the six states in the Chesapeake Bay watershed (Delaware, Maryland, New York, Pennsylvania, Virginia and West Virginia) and the District of Columbia are continuing to help decrease pollution in the Bay and reduce the size of the dead zone.

Throughout the year, researchers measure oxygen and nutrient levels as part of the Chesapeake Bay Monitoring Program, a Bay-wide cooperative effort involving watershed jurisdictions, several federal agencies, 10 academic institutions and over 30 scientists. Among these institutions, the Maryland Department of Natural Resources and Virginia Department of Environmental Quality conduct 8-10 monitoring cruises between May – October to keep an eye on the dead zone. The results of the monitoring cruises are posted on the Eyes on the Bay website for the Maryland portion of the Bay and the VECOS website for the Virginia portion. Estimates of river flow and nutrients entering the Bay can be accessed on the U.S. Geological Survey’s website. Scientists at the Virginia Institute of Marine Science (VIMS) also produce daily, real-time estimates of the size of the dead zone for the entire Bay.