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 2021 Chesapeake Bay dead zone

In the annual Dead Zone Report Card, the Virginia Institute of Marine Science (VIMS) announced that the 2021 Chesapeake Bay dead zone covered an average of 1.5 cubic miles during the summer, slightly larger than most recorded in the past 36 years (67%). Overall, the 2021 dead zone lasted for 141 days—46 days longer than 2020. In the short-term, experts believe that several factors, including calm winds, increased precipitation and warm temperatures throughout the late summer of 2021 contributed to the larger dead zone. In fact, the months of August and September were recorded as the fifth hottest on record for the state of Maryland, according to the National Oceanic and Atmospheric Administration’s National Centers for Environmental Information. 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. However, warming from climate change may increase the dead zone's duration and size.

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.