The Chesapeake Bay’s hypoxia levels in 2024 remained near or below historical averages, according to data from the Maryland Department of Natural Resources (DNR) and Old Dominion University. Hypoxia, defined as waters with less than 2 mg/L of oxygen, affects aquatic life by creating low-oxygen zones, or “dead zones,” that limit habitats for crabs, fish, and oysters.
In 2024, hypoxic conditions in the Chesapeake Bay’s mainstem were larger than average in May and early June but declined significantly by late summer. By October, no hypoxia was detected, marking the 30th time in 40 years that the Bay experienced no hypoxic conditions during the month. A full report by the Chesapeake Bay Program compared these findings with predictions, revealing slightly better oxygen levels than forecasted for the year.
2024 Hypoxia Data Highlights
Monthly monitoring cruises provided the following hypoxia volumes compared to the historical averages (1985–2023):
| Month | 2024 Hypoxic Volume (cubic miles) | Historical Average (cubic miles) | 2024 Rank (Least to Most Hypoxic) |
|---|---|---|---|
| May | 0.42 | 0.18 | 35th of 40 |
| Early June | 1.03 | 0.90 | 24th of 36 |
| Late June | 0.76 | 1.27 | 9th of 34 |
| Early July | 1.20 | 1.59 | 11th of 39 |
| Late July | 0.82 | 1.62 | 5th of 39 |
| Early August | 0.26 | 1.31 | 1st of 37 |
| Late August | 0.77 | 1.07 | 10th of 40 |
| September | 0.56 | 0.41 | 26th of 40 |
Mechanical issues with research vessels and adverse weather conditions during July and August likely caused underreporting of hypoxic volumes, especially in key monitoring zones. Despite these challenges, hypoxia levels remained near average throughout the summer.
Dead Zone Trends and Factors
The Chesapeake Bay’s dead zone began forming in late April and peaked in June and July. Strong winds from Hurricane Debby in early August mixed oxygen into deeper waters, contributing to a significant reduction in hypoxia for the remainder of the season. By September, hypoxic conditions were slightly above average, but no hypoxia was detected in October sampling.
Forecast Accuracy and Nutrient Management
The U.S. Environmental Protection Agency’s Chesapeake Bay Program, in collaboration with other institutions, predicted a 4% larger hypoxic volume than the long-term average due to higher river flows and nitrogen loads from January to May. However, monitoring data revealed better dissolved oxygen conditions than forecasted.
Ongoing nutrient management efforts have played a critical role in reducing nitrogen and phosphorus pollution, which are the primary drivers of hypoxia. These pollutants fuel algal blooms that deplete oxygen when they decompose, creating low-oxygen zones that harm aquatic ecosystems.
“The past few years of near or below average Bay-wide hypoxia levels are a good sign that Chesapeake Bay nutrient management actions are working,” said Dr. Marjy Friedrichs, a research professor at the Virginia Institute of Marine Science. However, she cautioned that these efforts must continue to counteract climate change’s impact on water quality.
Future Challenges
Despite recent progress, the Chesapeake Bay states are unlikely to meet their pollution-reduction commitments by the 2025 deadline. Regional leaders will convene at the Chesapeake Executive Council meeting on December 10 in Annapolis, Maryland, to chart a new course for Bay restoration efforts. Advocates, including the Chesapeake Bay Foundation, emphasize the importance of regional cooperation and updated goals to tackle pollution and ensure the health of the Bay.
“Bay restoration science continues to evolve, highlighting ways we can be more efficient and targeted in our pollution reduction efforts,” said Alison Prost, Vice President for Environmental Protection and Restoration at the Chesapeake Bay Foundation. “At this December meeting, we must see leadership, partnership, and accountability.”
Looking Ahead
The Chesapeake Bay’s hypoxia levels underscore both the progress made and the work ahead. Efforts to address nutrient pollution, adapt to climate change, and enforce accountability will be critical in ensuring the long-term health of the Bay.
