Chesapeake Bay hypoxia — waters with less than 2 milligrams of oxygen per liter — remained well below average in early August 2026 before rising to just above the long-term average by late August, according to data collected by the Maryland Department of Natural Resources and Old Dominion University.
Early August’s hypoxic volume ranked as the fifth-smallest observed for that time period in more than three decades of monitoring, following the eighth-smallest late-July volume on record. By late August, however, hypoxic volumes had climbed to 1.12 cubic miles, just above the 1.06 cubic-mile long-term average for that period — a shift from the sharply below-average conditions that defined most of the summer.
The pattern extends a season-long trend of milder-than-usual dead zone conditions in the Bay’s Maryland and Virginia mainstem, one the Chronicle has tracked since a May forecast predicted a smaller-than-average dead zone for summer 2026.
Season Summary
Combined Maryland and Virginia mainstem Bay monitoring cruises recorded the following hypoxic volumes, in cubic miles, compared with the 1985-2025 average:
| Cruise | 2026 Volume | Average (1985-2025) | 2026 Rank |
|---|---|---|---|
| May | 0.0 | 0.18 | 1st (tied) of 42 |
| Early June | 0.076 | 0.85 | 1st of 38 |
| Late June | 0.97 | 1.27 | 14th of 36 |
| Early July | 1.48 | 1.61 | 21st of 41 |
| Late July | 1.08 | 1.60 | 8th of 41 |
| Early August | 0.67 | 1.30 | 5th of 39 |
| Late August | 1.12 | 1.06 | 28th of 42 |
Anoxia — waters with less than 0.2 milligrams of oxygen per liter, a more severe form of oxygen depletion — measured 0.23 cubic miles in early August and 0.25 cubic miles in late August, both lower than July’s anoxia volumes.
Drought a Key Factor
DNR attributes the better-than-average conditions in part to ongoing drought in the Chesapeake watershed, which has reduced the volume of water — and the nutrient pollution it carries — flowing into the Bay. Lower nitrogen and phosphorus loading means less fuel for the algal blooms that die off, decompose and strip oxygen from deeper Bay waters.
The Chesapeake Bay Program partners’ seasonal forecast, released in May by scientists from William & Mary’s Batten School of Coastal & Marine Sciences/VIMS, the University of Michigan, USGS and other partners, predicted Bay hypoxia volumes would run about 31% below the long-term average this year — a forecast that has held up closely against the monitoring data collected so far. That forecast was based in part on river-flow and nutrient data from January through April 2026, when flow into the Bay ran 32% below the long-term average and nitrogen loading was 39% lower than average, or about 59 million pounds.
The results build on a season the Chronicle has followed cruise by cruise, from May and June’s record-low volumes through July’s continued below-average conditions.
Crabs, fish, oysters and other Bay species require dissolved oxygen to survive, and scientists and resource managers track hypoxia’s volume and duration to gauge potential impacts on Bay life. DNR computes hypoxia volumes each year from May through October using water quality data managed by department staff and the Virginia Department of Environmental Quality, with data collection funded by both states and the Chesapeake Bay Program. Monitoring and reporting will continue through the summer.
Additional water quality data and DNR’s hypoxic volume calculation methods are available on the Eyes on the Bay website.
