EASTERN SHORE, Va. — A sprawling harmful algal bloom that moved into waters along Virginia’s Eastern Shore in September has left oyster growers confronting potentially devastating losses, coincided with fish kills in at least seven local creeks and renewed questions about whether better monitoring and earlier warnings could help protect one of the Shore’s most important industries.
The mahogany bloom spread through bayside waters along the southern Eastern Shore, prompting the Virginia Department of Health on Sept. 21 to advise people and pets to avoid contact with discolored water. VDH said the bloom itself is not considered harmful to people, although dense concentrations of algae can cause skin irritation. The algae can, however, produce toxins harmful to fish, and dense blooms can contribute to fish kills by reducing dissolved oxygen in the water.
The economic damage may be substantial.
Oyster growers have reported significant mortality among market-size oysters, younger grow-out oysters and oyster seed.
The losses are potentially significant beyond individual farms. Virginia ranks first nationally in the production of hard clams and Eastern oysters, according to information cited by Virginia’s congressional delegation, and shellfish aquaculture generated approximately $81 million in direct farm sales in the Commonwealth in 2024.
Researchers at the Virginia Institute of Marine Science said the bloom expanded from the mainstem Chesapeake Bay into nearshore waters along the bayside of the Eastern Shore. VIMS collected samples from what researchers described as a near-continuous bloom stretching from Cape Charles north to south of Nassawadox Creek, with bloom activity also documented in Nassawadox, Hungars and Cherrystone creeks.
The bloom includes Alexandrium monilatum, commonly called “Alex,” a species capable of harming fish, shellfish and other marine organisms.
But scientists have cautioned against jumping from correlation to causation.
VIMS said the bloom coincided with widespread fish kills and reports of oyster mortality and that Alexandrium monilatum is known to have harmful effects on aquatic organisms. Researchers, however, are still collecting and analyzing data to determine the relationship between the bloom and the mortality observed on the Eastern Shore.
That distinction matters as attention turns to what caused the event.
Blooms Are Not New — or Necessarily Man-Made
Algal blooms are natural phenomena, and algae themselves are a normal and essential part of aquatic ecosystems. Most species are harmless.
NOAA says blooms can develop or intensify under a complicated combination of environmental conditions, including favorable winds and currents, sluggish water circulation, unusually warm water and extreme weather. Sunlight, nutrients and slow-moving water can all create favorable conditions for rapid algal growth.
The species involved in the Virginia bloom is not new to the Chesapeake Bay. VIMS conclusively identified Alexandrium monilatum in the Bay in 2007, and blooms have occurred nearly every year since, generally during late summer.
That history makes it important not to automatically attribute this month’s event to a single pollution source or human activity. VIMS says researchers are still investigating the specific conditions that caused the bloom to move toward the Eastern Shore and intensify.
At the same time, naturally occurring blooms and nutrient pollution are not mutually exclusive issues.
NOAA and the Environmental Protection Agency say excessive nitrogen and phosphorus entering waterways from agriculture, lawns, wastewater, stormwater and other sources can stimulate algal growth and make some blooms larger or more severe. Fertilizer that washes from lawns or farm fields during rainfall is one potential source of those nutrients.
When algae die and decompose, that process can consume dissolved oxygen. If oxygen concentrations fall far enough, hypoxic — or “dead zone” — conditions can develop in which fish, shellfish and other aquatic organisms struggle to survive.
The same basic principle makes responsible fertilizer use important even when fertilizer has not been identified as the cause of a particular bloom. Excess fertilizer left on lawns or fields can be carried by rain into storm drains, creeks and other waterways. EPA recommends applying fertilizer in appropriate amounts, at appropriate times and using methods that minimize nutrients escaping into surrounding waters.
Federal Assistance Sought
The scope of the oyster losses has now drawn the attention of Virginia’s congressional delegation.
U.S. Reps. Jen Kiggans and Rob Wittman sent a Sept. 25 letter to Agriculture Secretary Brooke Rollins asking the U.S. Department of Agriculture’s Farm Service Agency to assess losses suffered by commercial oyster growers and determine whether the event could qualify for a Secretarial natural disaster designation.
Such a designation could make eligible oyster producers in affected and adjoining counties eligible to apply for federal emergency farm loans, although assistance would not be automatic and individual producers would still have to meet program requirements.
The lawmakers also called for USDA to coordinate with VIMS, Virginia Tech and other state and federal scientific agencies to determine the extent and cause of the mortality.
The potential consequences extend beyond oysters ready for market. Losses of juvenile and seed oysters could affect future production as well, meaning some growers could feel the financial impact long after the reddish water disappears.
Could Earlier Warning Reduce the Damage?
The episode is also raising another practical question for the Eastern Shore: whether growers can be given more warning when a dangerous bloom is moving toward local aquaculture grounds.
NOAA was tracking bloom activity in the mainstem Chesapeake Bay before high concentrations of Alexandrium were detected along the Eastern Shore, according to VIMS. Researchers are now monitoring the bloom and coordinating with shellfish farmers.
Improved monitoring and forecasting would not prevent a naturally occurring bloom. It could, however, potentially give growers additional time to take protective measures where those measures are practical. NOAA says one goal of harmful-algal-bloom forecasting is precisely that — providing coastal communities advance warning so they can prepare for environmental and health impacts.
Virginia already maintains a Harmful Algal Bloom surveillance system, and VIMS operates an oyster crop mortality reporting program that collects weekly information from participating commercial growers. Those systems could provide a foundation for examining whether faster notification, expanded sampling or more localized forecasting could reduce the economic consequences of future events.
For now, scientists are continuing to investigate what happened.
The Eastern Shore event illustrates the complexity of harmful algal blooms. They existed long before modern agriculture, suburban lawns or wastewater systems, and natural changes in temperature, circulation and weather can produce favorable conditions for blooms. At the same time, decades of research have established that excess nutrients entering waterways can worsen algal growth under the right conditions.
Determining which factors drove this particular bloom will require evidence rather than assumptions.
For Eastern Shore oyster growers staring at dead inventory, however, the immediate issue is less theoretical. A crop that can take years to reach market size can disappear in days, and September’s bloom has demonstrated just how quickly an environmental event in the Chesapeake Bay can become an economic crisis on the Shore.
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