{"id":6318,"date":"2024-07-17T13:08:20","date_gmt":"2024-07-17T17:08:20","guid":{"rendered":"https:\/\/www.vdh.virginia.gov\/blue-ridge\/?page_id=6318"},"modified":"2026-01-14T15:03:16","modified_gmt":"2026-01-14T20:03:16","slug":"harmful-algal-blooms-2","status":"publish","type":"page","link":"https:\/\/www.vdh.virginia.gov\/blue-ridge\/harmful-algal-blooms-2\/","title":{"rendered":"Harmful Algal Blooms"},"content":{"rendered":"

What are Harmful Algal Blooms (HABs)?<\/strong><\/span><\/h3>\n


\n<\/strong><\/span>Algae are microscopic organisms that can be found in coastal and fresh waters. They are major producers of oxygen and food for many of the animals that live in these waters. When environmental conditions are favorable for their development, these cells may multiply rapidly ; this is called an algal bloom. A bloom often results in a change of water color. Algal blooms in coastal waters are usually red or brown, while in freshwater they tend to be green, blue-green, and less commonly red. Most algal blooms are not harmful but some may affect fish and humans, as well as other animals like birds and marine mammals. These are known as Harmful Algal Blooms (HABs). Definitions of a HAB may vary. The Task Force priorities the protection of human health during HAB events.<\/p>\n

What causes algae blooms?<\/span>
\n<\/strong>Blooms are usually a result of too much nutrients in the water. Nutrients end up in the water as a result of pollution from nonpoint sources \u2013 such as runoff from the land and discharges. Water temperature has also been related to the occurrence of algal blooms, with unusually warm water being conducive to blooms. Algae use the light energy of the sun and chemical energy of nutrients to make their own food. Waterbodies with a large surface area exposed to the sun, like lakes and estuaries, are more prone to algal blooms.<\/p>\n

Algae Blooms in Chesapeake Bay<\/span>
\n<\/strong>The Chesapeake Bay is a productive ecosystem, with abundant fish and shellfish resources that rely on algae to feed. \u00a0Seasonal weather cycles,\u00a0including changes to temperature and precipitation,\u00a0lead to fluxes in both the total amount of algae, as well as the species composition throughout the year. \u00a0In general, summer and fall seasons in Chesapeake Bay include blooms of a number of\u00a0different algae that tend to discolor the water leading to red and brown tides.<\/p>\n

What is known about the Seasonal Blooms in Lower Chesapeake Bay?<\/strong><\/span><\/p>\n

The type of algal species<\/strong>: In particular, two types of algae are responsible for extended and widespread red\/brown tides in Virginia waters:\u00a0Margalefidinium\u00a0polykrikoides<\/em>\u00a0and\u00a0Alexandrium\u00a0monilatum<\/em>. \u00a0These bloom species have been observed\u00a0in the lower York and James Rivers and lower Chesapeake Bay annually in July-October\u00a0most years for at least the last 10-15 years.<\/p>\n

That these particular species have\u00a0not<\/u>\u00a0been tied to human health impacts<\/strong>: While these blooms discolor the water and may be associated with foul odors, they have\u00a0not\u00a0<\/u>been tied to human health impacts.<\/p>\n

That these particular species have been linked to\u00a0fish kills\u00a0and die offs of oysters and other shellfish resources.<\/strong>\u00a0\u00a0These can be attributed to low oxygen conditions or the production of compounds and toxins that impact fish and shellfish.<\/p>\n

How are HABs dangerous to fish and humans?<\/strong><\/span>
\n<\/strong>HABs are dangerous to fish because they can deplete oxygen in water. When oxygen levels become too low, fish suffocate and die. Some algae species in blooms produce toxins that can kill fish and cause illness in humans.<\/p>\n

How do you get exposed to HAB toxins?<\/strong><\/span>
\nMost illness associated with HAB exposure is the result of consuming toxins that are present in shellfish or finfish. Recreational contact with water (such as swimming) during a bloom may result in illness as well. This may be due to accidental ingestion, from skin contact, or inhalation of aerosolized HAB toxins due to wind and wave action.<\/p>\n

Are HABs in Virginia?<\/strong><\/span>
\nAlgal blooms do occur in Virginia but blooms that are composed of harmful species of algae are reported rarely in Virginia. Virginia\u2019s coastal waters are monitored for HABs because it is important to be aware of them when they happen to protect public health.<\/p>\n

Is it safe to eat seafood?<\/strong><\/span>
\nIn general, it is safe to eat seafood. However, consuming shellfish that have been harvested from waters with high levels of harmful algae and consuming fish that have lesions or that were caught in an area during an algal bloom can result in illness.<\/p>\n

In freshwater, fish caught from a waterbody with a bloom are safe to consume, providing the filet is cleaned, the carcass and internal organs are discarded, and the fish is cooked to proper temperature. There is research that suggests in waterbodies with ongoing and persistent toxin blooms, that fish can accumulate toxins in the muscle tissue (filet). However, in Virginia, there are no known waterbodies which have persistent, toxin blooms of this magnitude. More study is needed to understand fish exposure as opposed to toxin accumulation in tissues within freshwater environments.<\/p>\n

What are the symptoms of exposure to HAB toxins?<\/strong><\/span>
\nSymptoms vary depending upon the toxin involved and the exposure route. Information on marine HAB toxins are available\u00a0here<\/a><\/span><\/span>.<\/p>\n

If I were to become sick from exposure to HABs, could I transmit disease to anyone?<\/strong><\/span>
\nThe illnesses cause by toxins from HABs are not spread from one person to another.<\/p>\n

What is Virginia doing about HABs?<\/strong><\/span>
\nThe Department of Environmental Quality and the Department of Health, including the Division of Shellfish Safety and Waterborne Hazards, work together to regularly monitor the water and shellfish growing areas for the presence of HABs and to conduct surveillance for human health effects. The public will be notified if a HAB that could affect human health is identified.<\/p>\n

VDH Shellfish Closures are What Stops Shellfish Harvest to Protect Public Health<\/strong><\/span><\/p>\n

The Virginia Department of Health (VDH)\u00a0works with the Virginia\u00a0Department of Environmental Quality\u00a0(DEQ), Old Dominion University and the Virginia Institute of Marine Science, as well as other state and federal partners to monitor HABs and protect public health through managing Virginia\u2019s shellfish growing areas. \u00a0A small number of HAB species that can produce toxins that accumulate in shellfish, and may pose a threat to human health,\u00a0are<\/strong> closely monitored by VDH, and shellfish closures would be issued as necessary to prevent shellfish poisoning<\/strong>.\u00a0\u00a0In fact, there has never been an algal toxin related human health illness from shellfish harvested in the state of Virginia<\/u>.<\/p>\n

How do I report a HAB and \/or a fish kill?<\/strong><\/span><\/p>\n

You may attach pictures of the water to help the Task Force evaluate the appearance of the bloom.<\/p>\n

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 may help him\/her treat the illness properly.<\/strong><\/p>\n

If you have health concerns, please contact your local health department or\u00a0your physician. You may report the incident to the HAB Hotline at (888)238-6154.<\/p>\n

Please submit your observations of algae or a fish kill using to our\u00a0HAB online report form.<\/span><\/span><\/a><\/p>\n

You can also call to report your observations to the HAB Hotline: 1-888-238-6154<\/strong><\/span><\/p>\n

VDH Resources List<\/a><\/span>\u00a0<\/strong><\/p>\n","protected":false},"excerpt":{"rendered":"

What are Harmful Algal Blooms (HABs)? Algae are microscopic organisms that can be found in coastal and fresh waters. 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