Underwater grass seen below the water.
Image by Will Parson/Chesapeake Bay Program

Overview

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.

Impact on Chesapeake wildlife

Plant and animal life are often unable to survive in hypoxic environments, which is why the area is referred to as a dead zone. Marine species like fish and crabs have to move away from these areas or swim above or below them in the water column. Incidents known as “fish kills,” when dead fish washup on shore, are often caused by dead zones in the water. Other species like oysters, which set up habitat in a specific location that cannot be moved, are particularly vulnerable to dead zones since they cannot relocate.

When and where do dead zones occur?

The dead zone is most pronounced in the deep waters of the Bay's mainstem because there is generally less oxygen toward the bottom of a body of water. Also, when algae die, they fall to the bottom of the water and remove oxygen. Dead zones most often occur during the warm summer months. This is due to the amount of rainfall that occurs during the spring, which washes excess nutrients off the land and into the water, as well as hot temperatures and weak winds in the summer which cause the dead zone to grow larger and last longer.

What is the size of the most recent dead zone?

Graphic showing that the 2021 dead zone was 1.5 cubic miles.
Data from Virginia Institute of Marine Science.

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.

How do we determine 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.

How is climate change impacting dead zones?

Climate change has caused the Chesapeake Bay region to have more severe rainstorms and warmer average temperatures. Both rainfall and high temperatures accelerate the algae blooms that lead to dead zones. In recent years, the Bay region has had above average rainfall and temperature that have both led to above-average dead zone sizes.

What’s being done to limit dead zones?

We can reduce the size and duration of summer dead zones by reducing the amount of sediments and nutrients that enters the Chesapeake Bay. Nutrients and sediment enter the water from both point-sources, such as wastewater treatment plants, and non-point sources, such as agriculture and urban areas. Implementing pollution reducing practices in both instances can help to reduce nutrients and sediment runoff, thereby limiting dead zones.

How you can help

While you may not be able to control the weather, there are actions you can take to control the amount of nutrient pollution entering the Bay and to help slow the rise of climate change. Consider reducing the amount of pollution that can run off your property by installing a rain garden or rain barrel to capture and absorb rainfall. Use boiling water to kill weeds and other pests, rather than use chemical pesticides in your garden or yard.

Partnership goals

The Chesapeake Bay Program is committed to reducing nutrient pollution through its 2025 Watershed Implementation Plans. As of 2021, practices in place to reduce pollution are estimated to achieve 49% of the nitrogen reductions, 64% of the phosphorus reductions and 100% of the sediment reductions needed to attain applicable water quality standards when compared to the 2009 loads.

Track our work at ChesapeakeProgress.com