The Maryland Department of Natural Resources (DNR) and Old Dominion University have reported smaller-than-average levels of hypoxia—waters with oxygen levels below 2 mg/L—in Maryland and Virginia’s Chesapeake Bay mainstem for early and late August. These findings, based on bi-state monitoring cruises, contrast with predictions from environmental agencies that had forecast higher hypoxic volumes in the Bay for the 2024 season.
Hypoxia in the Chesapeake Bay is closely monitored as it poses risks to aquatic life, including fish, crabs, and oysters, all of which rely on oxygen-rich waters for survival. Hypoxic conditions are typically triggered by algal blooms, which, upon decomposing, deplete oxygen levels in the water. Monitoring hypoxia provides crucial data for understanding the health of the Bay and for evaluating the efficacy of ongoing nutrient pollution reduction efforts.
The following table summarizes hypoxic volumes recorded during 2024 compared to historical averages from 1985 to 2023:
| Cruise Period | 2024 Hypoxic Volume | Historical Average Hypoxic Volume | 2024 Rank (out of Years Monitored) |
|---|---|---|---|
| May | 0.42 cubic miles | 0.18 cubic miles | 35th out of 40 |
| Early June | 1.03 cubic miles | 0.90 cubic miles | 24th out of 36 |
| Late June | 0.76 cubic miles | 1.27 cubic miles | 9th out of 34 |
| Early July | 1.20 cubic miles | 1.59 cubic miles | 11th out of 39 |
| Late July | 0.82 cubic miles | 1.62 cubic miles | 5th out of 39 |
| Early August | 0.26 cubic miles | 1.31 cubic miles | 1st out of 37 |
| Late August | 0.77 cubic miles | 1.07 cubic miles | 10th out of 40 |
In a season forecast issued in late June, the U.S. Environmental Protection Agency’s Chesapeake Bay Program, U.S. Geological Survey, University of Maryland Center for Environmental Science, and the University of Michigan projected that hypoxic volumes would rise by about 4% over the 39-year average. The prediction was based on observed river flows and nitrogen load increases from January to May 2024. However, data gathered from the Bay over the summer indicated a better-than-expected oxygen level, resulting in less extensive hypoxia than anticipated.
Unforeseen Challenges in Data Collection
Data collection this summer faced significant challenges due to mechanical issues with research vessels and adverse weather conditions. In July, Maryland stations CB5.3, LE2.3, and CB5.2 were not sampled due to vessel-related issues, and Virginia stations CB7.1N and CB7.3 also went unsampled due to poor weather conditions. Similar issues in early August prevented sampling at Virginia sites CB5.4, CB5.4W, CB5.5, CB6.1, CB6.2, CB6.3, LE3.6, and LE3.7.
Despite these interruptions, the data collected reveals that, with the exception of early measurements in May and June, hypoxic volumes have generally been below the historical averages. Early August showed an exceptionally low hypoxic volume, measuring at just 0.26 cubic miles—the smallest volume on record for that period since monitoring began. Late August also recorded a smaller hypoxic volume than average, ranking 10th out of the past 40 years.
Implications for Chesapeake Bay Health and Restoration Efforts
Reducing hypoxic conditions is central to restoration initiatives in the Chesapeake Bay, as oxygen is a critical factor for the survival of fish, shellfish, and other aquatic life. Hypoxia is driven by nutrient pollution, primarily nitrogen and phosphorus, which enter the Bay from sources such as industrial facilities, agricultural land, wastewater, and urban runoff. These nutrients stimulate algae growth, and when the algae die and decompose, oxygen is consumed, leading to hypoxic zones.
Ongoing efforts by Maryland, Virginia, and various environmental agencies aim to curb nutrient runoff and improve water quality. The states continue to invest in infrastructure and pollution control strategies to reduce nitrogen and phosphorus levels entering the Bay, with the goal of minimizing hypoxic volumes and supporting a healthier ecosystem.
The Maryland Department of Natural Resources, in collaboration with the Virginia Department of Environmental Quality, calculates hypoxic volumes from May through October each year, funded in part by the Chesapeake Bay Program. A comprehensive report comparing the 2024 hypoxic data to forecasted values is expected this fall.
For more information on Maryland’s water quality data, including detailed hypoxia monitoring methods, visit the Eyes on the Bay website.
