November 20, 2024: The dead zone in the Chesapeake Bay, a low-oxygen area that can smother underwater life, was about average in size in 2024, according to data released by the Chesapeake Bay Program. Read more

What Is a Dead Zone?

Dead zones are areas in bodies of water like the Chesapeake Bay that have little to no oxygen. Fish, crabs, oysters and other aquatic life literally suffocate in these zones.

What Causes Dead Zones in the Chesapeake Bay?

Dead zones are caused by excessive nitrogen and phosphorous pollution from human activities, including:

• Agricultural runoff from farmland that carries nutrients from fertilizers and animal manure into rivers and streams, eventually flowing into the Chesapeake Bay.
• Urban/suburban runoff from developed areas that washes nutrients from fertilizers, septic systems, and other pollutants into local waterways that flow downstream into the Chesapeake Bay.
• Wastewater treatment plants that release treated water—often still containing large amounts of nutrients—into streams and rivers across the watershed that flow into the Chesapeake Bay.
• Air pollution from our cars, factories, gas-powered tools, and power plants that contribute nearly 30 percent of the total nitrogen pollution to the Bay's waterways.

When there are excessive amounts of nitrogen and phosphorus in the water, algae can bloom to harmful levels. Dead zones form when the algae die, sink to the bottom, and are decomposed by bacteria—a process that strips dissolved oxygen from the surrounding water. Dense algal blooms also block sunlight, which prevents underwater grasses from growing. In turn, the animals that depend on these grasses for food and shelter suffer, as well.

Once a dead zone forms, other factors can influence its size and duration. For example, wind can mix oxygen from the surface into deeper water and help break up dead zones. Hot temperatures can make dead zones worse by warming a layer of surface water that locks colder, denser water below where oxygen from the surface can’t mix in. Heavy rainfall increases the amount of pollution washed into waterways.

But while weather can play a role, the best way to reduce algal blooms and dead zones is to stop pollution at its source by implementing the Chesapeake Clean Water Blueprint.

Where Are the Dead Zones in the Chesapeake Bay? 

Dead zones form in both the Bay’s mainstem and its tidal rivers, typically in deeper water near the bottom. The location, extent, and severity of the dead zones can change throughout the year, usually peaking during the summer months. There can also be significant variation from year to year due to changes in weather. For example, a rainy spring can wash more pollution into rivers like the Susquehanna, the Bay’s largest tributary, leading to a bigger dead zone that year.

How Big Are the Dead Zones in the Chesapeake Bay?

On average, the Chesapeake Bay dead zone covers between 1.2 cubic miles during the summer months, when the water is warmest and oxygen levels are historically lowest. Long-term trends indicate the Bay's dead zones are getting smaller.

Water monitoring data collected by the Maryland Department of Natural Resources, Old Dominion University, and Virginia Institute of Marine Science showed the smallest recorded dead zone—an average 0.52 cubic miles during May-October 2023— since monitoring began 39 years ago.

How Do Dead Zones Affect People Living Around the Chesapeake Bay?

Dead zones are not a direct threat to humans, but they are extremely harmful to fish, crabs, oysters, and other aquatic animals that humans rely on for seafood and livelihoods. For example, researchers at VIMS have hypothesized that the Bay’s dead zone contributes to stress and disease in striped bass, loss of animals from the bottom of the Bay’s food chain, and a reduction in nutrition for predators, as bottom dwellers’ growth is stunted by lack of oxygen.  

In addition, the algal blooms that fuel dead zones can be detrimental to tourism and recreation. Harmful algal blooms can make water unsafe for swimming by generating toxins, release unpleasant odors, and cause fish kills that can wash hundreds of dead fish onto beaches.

It’s unhealthy for the Bay, it’s harmful to local economies, and it’s fixable.

The best way we can reduce algal blooms and dead zones is to implement the Blueprint by putting in place best management practices that control pollution from urban and agricultural lands, as well as wastewater treatment plants and septic systems. This includes things like planting trees as buffers along rivers and streams, improving soil health on farms, reducing the amount of hard surfaces in cities, and upgrading wastewater treatment plant technology.

Together, and only together, can we prevent dead zones and ensure vibrant habitats for aquatic life in the Chesapeake Bay.

What YOU Can Do to Prevent Dead Zones

Restoring the Bay and preventing future dead zones go hand in hand. Here are actions you can take to fix the dead zones in the Chesapeake Bay:

• Support our Bay-saving work. Make a donation to help CBF continue the fight to stop the pollution that causes dead zones.
• Join our action network and let your elected officials know you care about clean water Get the latest updates on local and federal actions you can take by signing up to receive our action alerts.
• Calculate your Bay Footprint, then take action at home.
• Drive less, walk/bike more!
• Before you fertilize your lawn, get a soil test. If your soil indicates you need fertilizer, make sure to sweep/blow it off the sidewalk/driveway/street back into your grass so it doesn't end up in the Bay. Fertilizing your lawn in the fall is also beneficial as you miss the heavy spring rains that drain to the Bay and it is when the fertilizer can do the most good to promote root growth (not top growth), so lawns are more drought resistant the following year.
• Make changes that reduce the amount of pollution that runs off your property. Install a rain barrel, build a rain garden, use porous pavers or gravel in place of paved surfaces. Direct your rain spouts into a rain barrel, rain garden, gravel swale, or—at the very least—onto your lawn, instead of your driveway.
• If you live near the water in Maryland or Virginia, become an oyster gardener.
• Support farms that practice regenerative agriculture.
• Learn more ways to get involved in saving the Bay.