FREQUENTLY ASKED QUESTIONS (FAQs): Alexandrium monilatum

Alexandrium monilatum Harmful Algal Bloom

Posted: September 19, 2016

What is an algal bloom?

Algae are naturally-occurring microscopic organisms that are found in fresh and salt waters of Virginia and around the world.  Algae species in fresh and salt water may multiply rapidly when environmental conditions are favorable for their development.  The great number of algal cells in the water results in what is called an algal bloom.

Algal blooms often result in a noticeable change in the color of the water.  They can be many colors, but are most commonly red or brown and are referred to as “red” or “brown” tides.  An odor may also be present in the vicinity of the bloom.

These “red tides” occur in Chesapeake Bay every summer, but have appeared earlier, wider, and more intense than in years past.  This is likely due to last winter’s warmth and this summer’s heat.  Red tides are caused by dense blooms of tiny marine plants called algae that contain reddish pigment.

How common are they?

Algal blooms are not uncommon in lower Chesapeake Bay during the spring and summer. Algae respond to the same conditions that encourage plant growth on land, and thus are most likely to form blooms when waters are warm and nutrient rich.

What type of algal bloom is occurring now?

Recent sample results in the lower York and James Rivers have shown a steady increase in the number of Alexandrium monilatum cells.  This alga is common in the Southern United States, but has also been seen recently in Virginia and the Chesapeake Bay since 2007.

Where are the blooms occurring now?

The A. monilatum bloom is currently occurring in the lower York River near Gloucester Point and Yorktown beaches, in the Lower James offshore of Norfolk Beaches, at the mouths of the James, and York Rivers, and in the Chesapeake Bay.  VDH Health Districts potentially affected by this bloom include Peninsula, Norfolk, Hampton, Portsmouth, Three Rivers, and Northampton.

What is the risk to public health?

Most algae do not harm people, wildlife, or the environment.  However, some types of algae in Virginia are dangerous and can affect fish and humans, as well as other animals like birds and marine mammals.  These are known as Harmful Algal Blooms (HABs).

Alexandrium monilatum is known to be toxic to fish at high levels, but there are no published studies that show this alga to be toxic to humans. Past and recent reports of laboratory and field staff exposure have shown temporary symptoms of watery eyes, runny nose, and mouth irritation during exposure. Field staff exposure has also shown symptoms of mild skin irritation.Reports of such effects have been uncommon and to-date, have only been reported by staff working in and around the dense areas of the bloom or in confined laboratory spaces. 

If you are concerned that you have been exposed to a HAB, please see your doctor or call your local health department.  Telling your doctor about contact with water and the specific location may help him/her treat any symptoms properly.

Is the bloom dangerous to pets?

It is not known if A. monilatum is harmful to pets.

Will this bloom impact shellfish?

Some algal species can impact shellfish; however, A. monilatum is not associated with any known toxins causing shellfish poisoning. The VDH Division of Shellfish Sanitation regularly monitors for toxin producing algae and can temporarily close shellfish harvest from areas affected by HABs to protect against shellfish poisoning.

What is being done to monitor the blooms?

During a bloom event, samples are analyzed for harmful species and/or algal toxins to determine any risk to human health or shellfish.  Several state partners are involved in regular monitoring for the presence of harmful algal blooms in the Eastern Region.  These include DEQ, VDH Shellfish Sanitation, VDH Division of Environmental Epidemiology, and Virginia Institute of Marine Science (VIMS), Old Dominion University (ODU) and other organizations.

Citizen reports of illnesses suspected of resulting from primary recreational contact with water are analyzed for surveillance of potential harmful algal blooms.

What should I do if I see an algal bloom?

Anyone who has observed a patch of water that is colored red or mahogany and is concerned should contact Virginia’s toll-free Harmful Algal Bloom hotline at (888) 238-6154.

Avoid swimming in areas with a visible bloom, or water with unusual color or odor, or if dead fish are observed in the swimming area. When in doubt, stay out. If you come in contact with the bloom, wash skin thoroughly with fresh water. If you are concerned about HABs and your health, please see your doctor and call your local health department.  Telling your doctor about contact with water and the specific location may help him/her treat any symptoms properly.

If you see a red or brown tide, water that has an odd color, or a fish kill, please call:

The Department of Environmental Quality – 757-518-2000          

If you see fish with lesions call:

The Virginia Institute of Marine Science – 804-684-7000

If you have health concerns, please call:

The Virginia Department of Health HABs Hotline: (888) 238-6154

VDH HAB Brochure