ANNAPOLIS — The Chesapeake Bay’s 2025 summer dead zone measured near long-term average levels, according to a new report released last week by scientists from the Virginia Institute of Marine Science and the Maryland Department of Natural Resources, even as regional leaders reaffirmed a 15-year commitment to reduce the pollution that creates these oxygen-starved waters.
The annual Chesapeake Bay Dead Zone Report Card found the hypoxic zone — where dissolved oxygen falls below 2 milligrams per liter, making survival difficult for fish, crabs, and oysters — reached typical size and duration despite variable weather conditions across the 64,000-square-mile watershed.
Heavy spring rains in parts of Pennsylvania and New York increased nutrient runoff into the Susquehanna River, the Bay’s largest tributary, while drier conditions in Virginia limited contributions from the Potomac and James rivers. Warm summer water temperatures, exacerbated by climate change, further reduced the Bay’s ability to hold oxygen.
Scientists measure the dead zone volume in cubic kilometers and track its extent from May through October. The 2025 average ranked neither among the smallest nor largest on record, falling close to the 1985-2024 mean calculated since systematic monitoring began four decades ago.
Excess nitrogen and phosphorus from agricultural fertilizer, wastewater, urban stormwater, and air deposition fuel massive algae blooms each spring and summer. When the algae die and sink, bacteria consume oxygen during decomposition, creating the low-oxygen conditions that force mobile species to flee and kill bottom-dwelling organisms.
The report’s release followed a Dec. 4 meeting of the Chesapeake Bay Program’s Principal Staff Committee and Executive Council in Washington, D.C., where governors from Maryland, Virginia, Pennsylvania, and Delaware, along with the mayor of the District of Columbia and the EPA administrator, formally adopted the 2025-2040 Chesapeake Bay Watershed Agreement Implementation Plan.
Maryland Governor Wes Moore, Pennsylvania Governor Josh Shapiro, Virginia Governor Glenn Youngkin, Delaware Governor Matt Meyer, and D.C. Mayor Muriel Bowser each signed the document recommitting their jurisdictions to the pollution-reduction targets established under the 2014 Chesapeake Bay Total Maximum Daily Load, a federally mandated cleanup plan enforced through the Clean Water Act.
The new implementation plan maintains the 2025 interim goal of having 60 percent of required practices in place and sets strategies to achieve full restoration by 2040, with particular emphasis on accelerating reductions from agriculture and addressing climate-change impacts.
Chesapeake Bay Foundation Senior Vice President for Programs Alison Hooper Prost welcomed the renewed commitment while stressing urgency.
“The dead zone is an existential threat to life in the Chesapeake Bay,” Prost said. “With climate change intensifying, now is the time to ramp up work to stop pollution from flowing into rivers and the Bay. Fortunately, governors from across the region just agreed to a 15-year Bay restoration plan. This agreement reinforces legal commitments to reduce the nitrogen and phosphorus pollution that feeds life-smothering dead zones.”
Prost added that decades of restoration experience and advancing science provide a clear path forward, provided governments deliver necessary policies and funding.
The Chesapeake Bay Program, established in 1983, coordinates restoration efforts among six states, the District of Columbia, and federal agencies. Maryland, Virginia, and Pennsylvania account for more than 90 percent of the remaining nutrient reductions needed to meet water-quality standards.
