Harmful Algal Blooms

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What is a Harmful Algal Bloom (HAB)?
What are the effects of cyanotoxins?
What do Harmful Algal Blooms look like?
What causes Harmful Algal Blooms?
What is WVDEP doing to address Harmful Algal Blooms?
What can I do if I see a potential Harmful Algal Bloom?
Have any Harmful Algal Blooms been reported in West Virginia?
Where can I view a list of previous HABs that have been reported in West Virginia?

What is a Harmful Algal Bloom (HAB)?
Microscopic algae are the base of the food web in aquatic systems, providing nutrients and oxygen for the higher trophic levels including benthic macroinvertebrates, fishes, and waterfowl. However, some of these algae are capable of producing toxins that can harm wildlife and/or humans. Algae blooms caused by species capable of producing toxins are called Harmful Algal Blooms or HABs.

Harmful Algal Blooms are a naturally occurring phenomena that can be found in nearly all aquatic environments, including lakes, ponds, rivers, and streams. Natural factors such as water temperature, pH, low water flows, light levels, and nutrient levels influence the growth and abundance of algae. Different algae species have different growth requirements and can bloom under different environmental conditions.  Many species of algae tend of bloom in the summer but blooms can occur year round. Some species of algae can produce toxins under certain conditions, many of which are not yet fully understood.

In freshwater systems, HABs are typically caused by a type of algae called cyanobacteria, or blue-green algae. However, not all cyanobacteria species cause HABs. Some common blue-green algae species capable of cyanotoxin production include: Microsystis, Dolichospermum (formerly Anabaena), Aphanizomenon, Planktothrix, and Lyngbya. Additionally, the presence of these species does not confirm the presence of toxins. Only certain strains, in certain ecological and environmental conditions produce toxins. Click here to see micrographs of common HAB-capable species of cyanobacteria and species-specific bloom descriptions.

Toxins produced by cyanobacteria are collectively referred to as cyanotoxins. These toxins can affect the liver, nervous system and/or the skin of people, pets, and wildlife. Children are more susceptible, than adults, to the effects of cyanotoxins.  Cyanotoxins may be present before a visible bloom, during a bloom, or after a bloom. Cyanotoxins may persist in the environment for months or years after a bloom. Cyanotoxins and/or cyanobacteria blooms can float downstream affecting other areas. Harmful Algal Blooms are not restricted to lakes; they can form in rivers and streams as well. However, Harmful Algal Blooms tend to occur in calm, stratified waters.

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What are the effects of cyanotoxins?
Cyanotoxins have a wide range of effects as hepatotoxins, neurotoxins, dermatoxins, and endotoxins. Symptoms vary depending on exposure route, duration, and toxin type/concentration.

Hepatotoxins damage the liver. Microcystin, Cylindrospermopsin, and Nodularin are hepatotoxins. Symptoms of exposure to hepatotoxins include abdominal pain, vomiting, diarrhea, liver inflammation, hemorrhaging, lesions, acute pneumonia, and death (within hours to days after exposure). Human cases are often reported from drinking water as well as ingestion of untreated/raw water, contact during recreational activities, and hemodialysis with toxin-laden water.

Neurotoxins are nerve toxins and include Anatoxin-a, Anatoxin-a(s), and Saxitoxins. Symptoms of exposure to neurotoxins include tingling, burning, numbness, drowsiness, staggering, incoherent speech, gasping, convulsions, and respiratory paralysis leading to death (within minutes to hours after exposure). Human deaths have been associated with shellfish consumption (saxitoxins). However, humans can be exposed to these toxins via recreational contact as well. Animal deaths, especially dogs, have been associated with recreational exposure. There is limited data available on neurotoxin exposure via drinking water.

Dermatoxins are skin toxins and include Lyngbyatoxin-a, Aplysiatoxin, and Lipopolysaccharides. Symptoms of exposure to dermatoxins are similar to swimmer’s itch and include skin rashes and eye irritations.

Cyanobacteria cell walls contain an endotoxin (lipopolysaccharide) that can irritate any exposed tissue and are capable of eliciting an immune response, including gastrointestinal distress and fever, when exposed to the intestines.
Harmful Algal Blooms (HABs) can be caused by many different types of cyanobacteria and therefore can have different appearances. Some HABs look like spilled paint, pea soup, foam, wool, streaks, or floating green globs. Colors may vary from green, blue-green, brown, white, purple, red, and black. Depending on the algae causing the bloom, surface scums may or may not be present and water may simply appear turbid (cloudy or muddy). See the photo gallery for pictures of Harmful Algal Blooms.
The exact mechanism for HABs is not well understood. However, in general, algae blooms typically occur during periods of warmer temperatures and increased sunlight, an abundance of nutrients, and low flow conditions.

Water Temperature
Many types of algae have an optimal growth temperature between 12°C and 15°C. However, the optimal temperature for most cyanobacteria growth is 25°C. When water is warmer than 25°C cyanobacteria can grow faster than other types of algae (ex. diatoms, green algae).

Light Availability
Cyanobacteria have adapted to flourish in variable and low light conditions unlike other types of algae. Some species of cyanobacteria, including the potential toxin producing Dolichospermum (formerly Anabaena), have gas vesicles that enable vertical movement through the water column. Adaptations such as gas vesicles allow movement toward optimal light concentrations and away from harmful light concentrations.

Low Wind/Low Flow Conditions
Water is more stable and less likely to mix during low wind and low flow conditions. With limited movement, lakes will thermally stratify; the top layer will heat up and without mixing the bottom will remain colder. The lack of mixing can lead to depletion of oxygen in the bottom layer, which can increase the release of nutrients from the bottom sediment.

Nutrients (Nitrogen and Phosphorus)
Typically, algae blooms, including cyanobacteria, are limited by phosphorus and/or nitrogen. An increase in the availability of nitrogen and/or phosphorus can lead to an algae bloom. Nutrients can wash into a lake or other waterbody from the surrounding environment. Many human activities including erosion from agricultural areas and lawns, deforestation, urban runoff, and sewage discharges can lead to nutrient enrichment of water and ultimately, an algae bloom.
West Virginia HAB Response Plan
A Harmful Algal Bloom Response Plan was developed as a joint effort by the West Virginia Department of Health and Human Resources (DHHR), the West Virginia Department of Environmental Protection, the West Virginia Division of Natural Resources, the U.S. Army Corps of Engineers, and Local Health Departments. The HAB Response Plan provides a unified statewide approach to address HABs in the recreational waters of West Virginia and to protect people and animals from toxins produced by HABs. This plan can be found here.

HAB Advisory Levels
In the event of a HAB with cyanotoxin levels above the Recreational Public Health Watch Advisory threshold, a public advisory will be issued and posted with an ORANGE sign. If toxin levels exceed the Recreational Public Health Warning Advisory threshold, a public advisory will be issued and posted with a RED sign. The table below contains the threshold limits for various cyanotoxins. Examples of the advisory signs are included below.

Threshold Level Microcystin*
General Information Signage <6 <80 <5 <0.8
Recreational Public Health Watch Advisory 6 80 5 0.8
Recreational Public Health Warning Advisory 20 300 20 3
*Microcystin and saxitoxin thresholds are intended to be applied to total concentrations of all reported variants/congeners of those cyanotoxins.

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What can I do if I see a potential Harmful Algal Bloom?
If you see a potential HAB in public recreational waters, report it either through the website http://tagis.dep.wv.gov/algae or complete an Algal Bloom Report Form and e-mail the form to West Virginia’s HAB mailbox at HAB@wv.gov. The form can be found here and in Appendix 5 of the HAB Response Plan.

If possible, submit digital photographs. Close-up (within 2 feet) and landscape photographs showing the extent and location of the algal bloom are helpful in HAB identification.
HABs reported in non-public (private) waters may be referred to Local Health Departments for assistance. For sampling in private waters, guidance provided in Appendix 7 and Appendix 8 of the HAB Response Plan can be used to collect samples. Samples can be sent to the West Virginia Office of Laboratory Services (OLS). Additional labs that perform phytoplankton identification and cyanotoxin analysis are listed in Appendix 9 of the Response Plan.

Once a report is received, depending on location, close monitoring and sampling will be conducted by either the WVDEP, WVDNR, or Local Health Departments. The standard sampling protocol can be found in Appendices 8 and 9 of the Response Plan. Sampling may include phytoplankton identification, cell quantification, assessments for the presence of toxins, and molecular assessment for the presence of cyanobacteria and/or cyanotoxin genes.

Have any Harmful Algal Blooms been reported in West Virginia?
Below are HABs that have been reported this year (last updated February 3, 2020). 


Bloom Location


Investigation Findings





 HAB Advisory Maps

There are no current HAB Advisories.  If a HAB Advisory were in place a map would appear below.  

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HAB Cyanotoxin Data

If a HAB is reported in 2020, links to view cyanotoxin data will appear below.