A mild dead zone is expected for the Chesapeake Bay this summer

Annapolis, Maryland—Scientists at William & Mary’s Batten School & VIMS, FlowWest and the University of Maryland Center for Environmental Science announced today that the Chesapeake Bay’s annual “dead zone” is expected to be relatively mild in summer 2026. According to the forecast, the severity of the dead zone is predicted to rank among the lowest 10% of years since extensive monitoring began in 1985 and will be about 31% below the long-term average.

“This year’s forecast suggests that the Chesapeake Bay may experience one of its milder dead zones in recent decades,” said Aaron Bever, senior managing scientist with FlowWest. “Lower nitrogen loads entering the Bay this spring are expected to translate into better oxygen conditions for fish, crabs, oysters and other Bay life this summer.” 

Dead zones in the Chesapeake Bay are areas of low-oxygen conditions where blue crabs, fish and other marine life struggle to survive. Hypoxia occurs when excess nutrients like nitrogen trigger large algal blooms that remove oxygen from the water after they die and decompose. 

This year’s mild outlook is largely due to low river flows and reduced nitrogen pollution entering the Bay from earlier in the year. From January through April 2026, the amount of water entering the Bay from rivers was 32% below the long-term average, while the amount of nitrogen was 39% lower than average, totaling about 59 million pounds of nitrogen, according to estimates from U.S. Geological Survey (USGS) monitoring stations. From this information, scientists forecasted the Bay’s total annual hypoxic volume, a metric that reflects both the extent of low-oxygen waters and how long those conditions last. This year’s total hypoxic volume is expected to be 31% lower than the long-term average.

Dr. Peter Tango, monitoring coordinator with the USGS at the Chesapeake Bay Program, said, “This mild year for dead zones is good news, especially compared with years when high river flow and nutrient loads have fueled much longer-lasting and larger areas of low-oxygen conditions.” 

While the forecast points to a relatively mild year, scientists note that summer weather conditions—such as heavy rainfall, heat waves or extended calm periods—can still influence the size and duration of the dead zone. These factors remain difficult to predict months in advance and contribute to some uncertainty in the forecast.

Extensive monitoring of the Bay’s hypoxia began in 1985 and the model for forecasting the severity of the summer dead zone was developed in 2007 by researchers at the University of Michigan. After multiple updates, the model is now used to estimate total annual hypoxic volume based on river flow and nitrogen input data provided by USGS. This year, funding for the forecast was provided by the VIMS Center of Excellence in Environmental Forecasting and the Mid-Atlantic Regional Association Coastal Ocean Observing System, a regional association of NOAA's U.S. Integrated Ocean Observing System.

“This forecast is part of a broader effort to make Chesapeake Bay science more useful and accessible,” said Dr. Marjy Friedrichs, research professor with W&M's Batten School of Coastal & Marine Sciences & VIMS. “Seasonal forecasts, real-time environmental predictions and fall assessments all help us understand how the Bay is responding to both management actions and year-to-year weather conditions.”

Chesapeake Bay Program partners work together to reduce the amount of nutrient runoff that enters the Bay from wastewater treatment plants, agricultural lands, urban and suburban landscapes and other sources through a variety of conservation practices. These efforts are helping to improve the health and resiliency of the Bay.

Researchers will conduct a full assessment of the dead zone’s extent and duration in fall 2026. Throughout the summer, conditions can be tracked through the Chesapeake Bay Environmental Forecast System and Maryland Department of Natural Resources Hypoxia Reports