2026 Dead Zone Update

 

from VIMS

The2026  “Dead Zone” began to build in May and rose steadily until early July when the peak in summer dead zone occurred. However, the size of the “Dead Zone” in the Bay has steadily declined since the peak in July. As of early August both the model-based and data-based estimates of hypoxia are point toward a relatively mild year for deep-water hypoxia in the Bay. This aligns with the forecast issued in the spring.

This year’s mild outlook was largely due to region wide drought with 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.

The “Dead Zone” of the Chesapeake Bay refers to a volume of hypoxic water that is characterized by dissolved oxygen concentrations less than 2 mg/L, which is too low for aquatic organisms such as fish and blue crabs to thrive. Within the hypoxic area life of the bay dies and a “Dead Zone” forms. The Chesapeake Bay experiences hypoxic conditions every year, with the severity varying from year to year, depending on nutrient and freshwater flows into the bay, wind, and temperature.

Each year the Maryland Department of Natural Resources measures the actual dissolved oxygen in the Maryland portion of the Chesapeake Bay main stem and the size of the Dead Zone. While the Virginia Institute of Marine Science (VIMS), Anchor QEA and collaborators at UMCES, operate a real-time three-dimensional hypoxia forecast model using measured inputs that predicts daily dissolved oxygen concentrations throughout the Bay (www.vims.edu/hypoxia) using the National Weather Service wind monitoring data.

The peak of oxygen depletion occurs in July or August when water temperatures are highest and the days are longest accelerating the growth of phytoplankton that ultimately consumes all the dissolved oxygen. The dead zone is typically gone by late fall. Cooler air temperatures at that time of year chill the surface waters, while the deeper water remains warm and allows more mixing of the layers during storms. Cooler water also will hold more oxygen. The size and shape of the dead zone is variable from month to month during the summer. So far this year is looking like a very promising year.

Real-time Estimates of Hypoxic Water Volume | Virginia Institute of Marine Science

At the end of the season the Virginia Institute of Marine Science (VIMS), Anchor QEA and collaborators at UMCES compile all the collected data to report the actual results.The report they prepared at the end of last year,  2025 Chesapeake Bay dead zone near long-term average | Virginia Institute of Marine Science says“… Similar to past years, the Bay’s dead zone expanded through June and peaked in July. However, it remained consistently high throughout July in comparison to past, more variable years. Elevated winds and cooler temperatures in early August helped reduce hypoxia in the Bay before the passage of Hurricane Erin in mid-August triggered a rapid decline. Hypoxia lingered at low levels through September before dissipating as temperatures cooled in the fall.”

“Even in what we classify as an average year, the Bay can experience periods of prolonged stress,” said Batten School of Coastal & Marine Sciences & VIMS Professor Marjorie Friedrichs. “July’s persistent hypoxia illustrates how sensitive the ecosystem is to subtle shifts in wind, temperature and river flow. Those changes can have real implications for the distribution and behavior of fish, crabs and other species that rely on well-oxygenated habitat.”

2025 Chesapeake Bay dead zone near long-term average | Virginia Institute of Marine Science