What are blue-green algae?
Blue-green algae, also known as Cyanobacteria, are a group of photosynthetic bacteria that many people refer to as "pond scum." Blue-green algae are most often blue-green in color, but can also be blue, green, reddish-purple, or brown. Blue-green algae generally grow in lakes, ponds, and slow-moving streams when the water is warm and enriched with nutrients like phosphorus or nitrogen.
When environmental conditions are just right, blue-green algae can grow very quickly in number. Most species are buoyant and will float to the surface, where they form scum layers or floating mats. When this happens, we call this a "blue-green algae bloom." Blue-green algae blooms generally occur between mid-June and late September, although in rare instances, blooms have been observed in winter, even under the ice.
Many different species of blue-green algae exist, but the most commonly detected include Anabaena sp., Aphanizomenon sp., Cylindrospermopsis sp., Microcystis sp., and Planktothrix sp. It is not always the same species that blooms in a given waterbody, and the dominant species present can change over the course of the season.
What can be done to reduce the frequency and intensity of blue-green algae blooms?
There are no quick or easy remedies for the control of blue-green algae once they appear in a lake or pond. Reducing the amount of nutrients that wash into our lakes and ponds will eventually reduce the frequency and intensity of blue-green algae blooms, but it may take a long time and a lot of community involvement to effectively change the nutrient concentrations in a water body. This is because there may still be large amounts of nutrients in the sediment at the bottom that may continue to serve as food for the blue-green algae.
Should I treat a blue-green algae bloom with a chemical to get rid of it?
No. Treatment of a surface water that is experiencing a blue-green algae bloom with an herbicide or algaecide may kill the blue-green algae, but any toxin(s) contained in the cells will be released at once, resulting in a slug of toxin(s) in the water. So while the bloom may no longer be visible, toxin(s) may be present for some period of time following treatment. It is best to stay out of a water experiencing a bloom and wait for the bloom to dissipate on its own.
Can blue-green algae make me sick?
Yes, it is possible for blue-green algae to cause illness. Blue-green algae are capable of producing several different toxins. People may be exposed to these toxins through contact with the skin (e.g., when swimming), through inhalation (e.g., when motor boating or water skiing), or by swallowing contaminated water. Types of toxins and potential health effects include the following:
Dermatotoxins and Gastrointestinal Toxins—These toxins affect the skin and mucous membranes, and can cause allergy-type reactions such as rashes, eye/nose/throat irritation, and asthma, as well as headaches, fever, and gastroenteritis (nausea, stomach cramps, vomiting, diarrhea). Examples include lyngbyatoxin and lipopolysaccharide endotoxins.
Hepatotoxins—These toxins affect the liver and other internal organs, and can cause gastroenteritis, tissue damage, muscle weakness, paralysis, and respiratory failure (with acute exposure), tumors, and possibly liver cancer (with long-term, chronic exposure). Examples include microcystins and nodularins.
Cytotoxins—These toxins also affect the liver and other organs (though through a different mode of action than hepatotoxins) and can cause malaise, headache, anorexia, vomiting, chromosome loss, DNA strand breakage, and damage to organs. An example is cylindrospermopsin.
Neurotoxins—These toxins affect the central nervous system and can cause seizures, paralysis, respiratory failure or cardiac arrest. Examples include anatoxin-a and saxitoxin. (Saxitoxin is the same toxin associated with red tide and paralytic shellfish poisoning in marine systems).
How do water treatment plants deal with blue-green algae?
While most municipal drinking water treatment plants with surface water supplies do not regularly monitor for algal toxins, they do use treatment techniques that would remove the toxins if they were present. Conventional water treatment facilities can remove the cells of algae and other growing organisms by adding chemicals that bind them together. As the cells clump together, they become heavier and fall to the bottom of settling basins. Additional removal is obtained by filtration and through the use of activated charcoal.
Can I eat fish from a lake with an ongoing blue-green algae bloom?
The World Health Organization advises that people who choose to eat fish taken from water where a blue-green algae bloom is present eat such fish in moderation and avoid eating the guts of the fish, where accumulation of toxins may be greatest. Also, take care to not cut into organs when filleting the fish and rinse the fillets with clean water to remove any liquids from the guts or organs before freezing or cooking.
Measures You Can Take to Protect Yourself
- Do not swim in water that looks like "pea soup", green or blue paint, or that has a scum layer or puffy blobs floating on the surface
- Do not boat, water ski, etc. over such water (people can be exposed through inhalation)
- Do not let children play with scum layers, even from shore
- Do not let pets or livestock swim in, or drink, waters experiencing blue-green algae blooms
- Do not treat surface waters that are experiencing blue-green algae blooms with any herbicide or algaecide-- toxins are released into the water when blue-green algae cells die
- Always take a shower after coming into contact with any surface water (whether or not a blue-green algae bloom appears to be present; surface waters may contain other species of potentially harmful bacteria and viruses)
Measures You Can Take to Help Reduce Future Blue-Green Algae Blooms
- Maintain native vegetation along shorelines as buffer areas
- Minimize activities that result in erosion
- Reduce the amount of fertilizer used on lawns
- Use only phosphorus-free fertilizer when possible
- Fix leaking septic systems
- Use only phosphorus-free detergents in dishwashing machines
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