Chesapeake Bay Monitoring Found Below Average Hypoxia in Early August and Near Average in Late August

Data collected by the Maryland Department of Natural Resources and Old Dominion University in August 2026 showed that volumes of hypoxia—waters with less than 2 mg/l of oxygen— were much smaller than average in early August, and near average in late August for the Chesapeake Bay mainstem of Maryland and Virginia. 

Hypoxia in early August was well below average, ranking as the 5th smallest mainstem hypoxic volume observed for that time period, and was preceded by the 8th smallest observed hypoxic volume in late July. Volumes increased in late August, however, to just above the long-term average.

Early and late August respectively had 0.23 and 0.25 cubic miles of anoxia—waters with less than 0.2 mg/l of oxygen, which was less than observed in July.

Summary results from combined Maryland and Virginia mainstem Bay monitoring cruises are as follows, with volumes in cubic miles. Rank is in order of lowest (better conditions) to highest hypoxia volume (worse conditions).

The better-than-average dissolved oxygen conditions this season are in part attributable to the recent and persistent drought conditions experienced in the watershed. This has led to lower water volumes flowing into the Bay, according to the U.S. Geological Survey, which means less nutrient pollution from phosphorus and nitrogen that fuels algal blooms that cause hypoxia in deeper Bay waters. 

The Chesapeake Bay Program partners’ seasonal dissolved oxygen forecast states “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 monitoring stations.” 

Monitoring results thus far align with the seasonal forecast, which predicted Bay hypoxia volumes will be about 31% below the long-term average. 

Crabs, fish, oysters, and other creatures in the Chesapeake Bay require dissolved oxygen to survive. Scientists and natural resource managers study the volume and duration of Bay hypoxia to determine possible impacts to Bay life.

Ongoing efforts to reduce nitrogen and phosphorus pollution from industrial and wastewater sources, agricultural land, and cities and towns are aimed at reducing hypoxic conditions in the Bay. In the water, nitrogen and phosphorus fuel algal blooms that remove oxygen from the water when they die off and decompose.

Each year from May through October, the Department of Natural Resources computes hypoxia volumes from the water quality data managed by department staff and the Virginia Department of Environmental Quality. Data collection is funded by these states and the Chesapeake Bay Program. Bay hypoxia monitoring and reporting will continue through the summer. Additional Maryland water quality data and information, including the Department of Natural Resources hypoxic volume calculation methods, can be found on the Eyes on the Bay website.