Dissolved oxygen conditions show improvement in late June and July

Data collected by the Maryland Department of Natural Resources and Old Dominion University show a higher than average volume of hypoxia—waters with less than 2 mg/l oxygen—in the Chesapeake Bay mainstem of Maryland and Virginia in early June, that improved to less than average size in late June though late July.

Summary results from Maryland and Virginia combined mainstem Bay monitoring cruises are as follows. 

* The ‘2024 Rank’ column indicates this year’s result rankings, from the least (better) to the most hypoxic volume, compared against historical results for each time period (number of years that monitoring was completed). Results are likely higher than reported for July 2024 because stations CB5.3, LE2.3, and CB5.2 in Maryland were not sampled due to mechanical issues with the research vessel, and Virginia stations CB7.1N and CB7.3 were not sampled due to adverse weather conditions.

These monitoring results also provide a comparison to the yearly seasonal forecast by the U.S. Environmental Protection Agency’s Chesapeake Bay Program, U.S. Geological Survey, University of Maryland Center for Environmental Science, and University of Michigan. This forecast, which was released in late June, expected 2024 Chesapeake Bay mainstem hypoxic volume to be 4% higher than the 39-year average, due to increased river flows and resultant higher nitrogen loads from January through May 2024. Results thus far indicate better dissolved oxygen condition than predicted.

Crabs, fish, oysters, and other creatures in the Chesapeake Bay require 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.