Blue-Green Algae (Cyanobacteria) Frequently Asked Questions

What are cyanobacteria?

Cyanobacteria, also known as blue-green algae, are bacteria which have some of the characteristics of plants. They are found throughout the world on land and in lakes, rivers, and ponds, and in estuaries and seawater (oceans). Cyanobacteria have an extensive fossil record - the oldest known fossils are found in rocks of Western Australia, dated 3.5 billion years old. Many unicellular cyanobacteria grow in colonies that are often surrounded by a gelatinous or mucilaginous sheath, whereas others grow as thread-like filaments. Morphologies in the group have remained much the same for billions of years.

Cyanobacteria were previously grouped with algae but are now classified as bacteria after analysis of cell structure and cell division. They differ from other bacteria in that they contain photosynthetic pigments similar to those found in algae and plants. Although they are predominantly photosynthetic (light-dependent) organisms, they are also capable of a using organic compounds as a source of energy. Some cyanobacteria have a specialized structure called a heterocyst that can fix molecular nitrogen. The ability to fix nitrogen gives these species a competitive advantage over other algae. Many cyanobacteria have gas vacuoles that allow them to remain in suspension and migrate to surface waters where there is plenty of light for photosynthesis. On the surface, colonies may clump together and form a scum which can cause water quality problems in lakes.

What is a cyanobacterial bloom?

A mass of algae in a body of water is called a bloom. Blooms are often found in standing water in lakes, ponds, ditches, lagoons, or embayments of rivers. Because many cyanobacteria species can regulate their buoyancy, they rise to the surface of the water and form a surface scum. A scum is a thin oily-looking film that can become several inches thick. When conditions are good for a bloom, a lake or pond can change from clear to turbid within just a few days.

When can blooms occur?

Most cyanobacterial blooms occur during warm summer months. However, toxic blooms can also occur during the colder winter months. American Lake in Pierce County, Washington, has a history of toxic episodes during the winter at low water temperatures (7-8oC). It is possible that a bloom can be found somewhere in Washington nearly any month of the year and at low water temperatures.

What causes a bloom?

Factors needed for bloom formation - whether toxic or not - are complex. No individual environmental cause or particular set of conditions clearly controls cyanobacterial bloom formation. Researchers have investigated factors such as light, temperature, percent oxygen saturation, nutrient availability and depletion, wind patterns, internal lake mixing, growth stage and zooplankton predation.

Three genera of cyanobacteria account for the vast majority of blooms: Microcystis, Anabaena, and Aphanizomenon. A bloom can consist of one or a mixture of two or more genera of cyanobacteria.

Cyanobacteria cannot maintain an abnormally high population for long and will rapidly die and disappear after 1-2 weeks. If conditions remain favorable, another bloom can replace the previous one in such a way that it may appear as if one continuous bloom occurs for up to several months.

How do I know if a bloom is toxic?

Not all cyanobacterial blooms are toxic. Even blooms caused by known toxin producers may not produce toxins or may produce toxins at undetectable levels. Since cyanobacterial toxins can be lethal to animals in relatively small amounts, caution should always be taken when a bloom occurs. As cells die, toxins are released into surrounding waters. Some toxins, such as microcystins, are very stable and can remain in the water for days or weeks after the bloom has disappeared. Scientists do not know what triggers toxin production by cyanobacteria.

Only laboratory tests can confirm whether a bloom is toxic or non-toxic.

Signs that a cyanobacterial bloom is toxic may include large numbers of dead fish, waterfowl, or other animals within or around a body of water. Terrestrial animals found dead may have algae around the mouth or on the feet and legs, indicating possible ingestion of and contact with a toxic bloom.

What should I do to get my lake tested?

Washington State Department of Ecology (Ecology) has a new Freshwater Algae Control Program. If you are a Washington state resident, the Washington Department of Ecology offers an algal identification service. If you think that your lake has an algae bloom and you want to have the algae identified, please contact Tricia Shoblom at the Washington Department of Ecology:

Telephone: (425) 649-7288
Email address:

Ecology is working with representatives of local health jurisdictions throughout the state to coordinate sample collection and shipping. If there is a bloom, you may be asked to collect a sample for phytoplankton identification and possible toxicity testing, although some counties prefer to have their staff collect samples.

How much does testing cost?

You or the local health jurisdiction will sample the lake and send the sample to the King County Environmental Laboratory (KCEL) in Seattle to identify algae and test for toxicity (microcystin-LR and anatoxin-a). The cost of sending the sample to the lab will be covered by you or the local health jurisdiction, if they collect the sample. The cost of testing for toxins and algal identification has been funded by Ecology.

What if a test is positive for toxicity?

If tests show that a bloom is toxic, county health officials will decide whether to post notifications of potential health concerns, close the lake for recreation, or wait for further testing.

Can testing ensure that all areas of the lake are safe?

No. Cyanobacterial blooms are known to be very patchy in nature. It is possible for higher cyanobacteria densities to be present in areas not surveyed, particularly along shorelines. Recreational users should avoid contact with water whenever surface concentrations of algae are evident or when the lake has an obvious green to blue-green appearance.

How is it determined when the water becomes safe once a bloom is reported?

Department of Health guidelines advise that a lake continue to be sampled and tested once a week for toxicity after toxin levels are above a certain concentration. Recreational use should be avoided until levels drop below the trigger concentration for two consecutive weeks. Local health officials will decide when to re-open the lake.

Why is this a concern to public health?

Cyanobacteria are an emerging public health issue for recreational waterbodies in Washington. Cyanobacterial blooms cause a variety of water quality problems, including fish kills, aesthetic nuisances such as odors and unsightliness, and unpalatable drinking water. Cyanobacterial blooms may also limit aquatic habitat for wildlife, impacting human recreational activities. Pets have died after exposure to toxic cyanobacterial blooms in Washington lakes.

Can cyanobacteria make me sick?

Yes. People may develop allergic reactions such as skin rash, hives, itchy eyes and throat if they come in contact with water containing cyanobacteria that are producing toxins. Swimming, water-skiing, and wind surfing are examples of recreational activities during which dermal exposure to toxins may occur. Some symptoms caused by cyanobacteria exposure may be similar to those caused by “swimmer's itch,” a condition that has been reported among bathers in many Washington lakes. Swimmer's itch may occur on any exposed skin and can cause a sharp burning and itching in affected areas. Small reddish bumps surrounded by a zone of redness may appear within twelve hours after swimming. Itching due to swimmer's itch is intense. If you come in contact with water containing blue-green algae toxins or swimmer's itch, rinse off your body as soon as possible.

Long-term exposure to water with microcystins has been shown to promote liver tumors in animals. For this reason, people and animals should not drink water from a source with a cyanobacterial bloom. It is possible for more severe illness to occur if cyanobacterial toxins are swallowed. Consult a physician if someone ingests water with cyanobacteria and has any of the following symptoms: stomach cramps, vomiting, diarrhea, fever, headache, and severe muscle or joint pain.

If someone shows signs of seizure or convulsions after swimming or drinking water where cyanobacteria are present, they should seek immediate medical attention.

What about children?

Children have less relative body weight than adults, a smaller quantity of the toxin may trigger an adverse response in a child's liver or central nervous system. Also, children may be at greater risk than adults because they may not be aware of any health risks due to a cyanobacterial bloom and may swallow water accidentally while swimming. Although teenagers and young adults may think that it is fun to play in the scums, this is not a good thing to do.

How can I be exposed?

You can be exposed to cyanobacteria and cyanobacterial toxins by swimming or drinking water where cyanobacteria are present. You can also be exposed by breathing air that contains cyanobacterial cells or toxins. Wind surfing, jet-skiing, boating, or watering lawns are activities where this might occur.

Dietary supplements contaminated with cyanobacterial toxins are another potential route of exposure. Bluegreen algae products are consumed in the United States, Canada, and Europe for their reported beneficial effects, including increased energy and elevated mood. Many of these products contain Aphanizomenon flos-aquae. Because M. aeruginosa coexists with A. flos-aquae, it can be accidentally collected during harvesting and can result in microcystin contamination of dietary products.

How can I minimize risks?

  • Avoid swimming, wading, wind surfing and water-skiing in waterbodies where cyanobacterial blooms are present.
  • Avoid drinking untreated surface water.
  • Follow advice provided by local health jurisdictions. These agencies generally post recreational areas with signs to inform the public of the presence of cyanobacterial blooms.

What kind of water treatment removes cyanobacterial toxins ?

According to EPA, water treatment techniques such as coagulation, sedimentation, filtration, disinfection, granular activated carbon, powdered activated carbon, ozonation, and ultraviolet radiation are effective to varying degrees at removing most common cyanobacteria and their toxins in drinking water. Close to 100 percent of particular toxins can be eliminated in finished water when the appropriate combination of techniques is used. However, some treatments such as copper sulfate can cause cells to disintegrate and produce increased toxin concentrations in surrounding waters. See the following link for more information: EPA Report 815-D-06-007 Chapter 15: Microorganisms on the CCL2 (PDF).

Can cyanobacteria make my pet sick?

Yes. Animals are also sensitive to cyanobacterial toxins. Pets and wildlife are likely to ingest algae when they drink water from a lake or pond with cyanobacteria. If toxins are being produced at the time animals drink the water, the animals can become very ill and even die.

Dogs can be exposed to toxins by licking cyanobacteria from their fur after swimming. Don't let pets or livestock swim or drink in areas where there is a scum or mat of algae on the water. If they do swim in such areas, rinse them off as soon as you can.

Symptoms of exposure to cyanobacterial toxins include loss of appetite, vomiting, weakness, seizures difficulty breathing and convulsions. Neurological symptoms, including salivation, can appear within 15 to 20 minutes of exposure. If your animals show any of these symptoms, seek veterinary advice. Be sure to tell your veterinarian that your animal may have come into contact with cyanobacterial toxins.

Should pets or livestock drink or swim in water containing algal blooms?

No. Animals can become extremely ill and die after swallowing water containing toxic cyanobacteria. The number of reports suggesting that algal toxins have played a role in the deaths of dogs has increased over the past decade.

In one of the first cases reported in Washington State, four pedigreed dogs died in September 1976 after drinking water from Long Lake near Spokane during a toxic Anabaena bloom. Other cyanobacterial blooms have been reported in eastern Washington, including a 1982 toxic bloom in Moses Lake that caused the deaths of two hunting dogs. In 1989, the first toxic cyanobacterial bloom west of the Cascade Mountains in Washington was documented in American Lake, Pierce County. This event caused the deaths of five cats. More recently, a toxic bloom in Lake Anderson, Jefferson County, Washington, caused the deaths of two dogs and a 2007 toxic bloom in the Potholes Reservoir that also caused the deaths of two hunting dogs.

Can I eat fish from contaminated water?

Microcystins can accumulate in fish tissues, especially in the viscera (liver, kidneys, etc.). Concentrations in the tissues would depend on the bloom severity where the fish was caught. Take caution when considering consumption of fish caught in a water body where major cyanobacterial blooms occur. Before eating, remove the internal organs, which may contain more of the algae/toxin.

Anadromous fish such as salmon and steelhead that migrate into a water body with a bloom may not have had an opportunity to concentrate much of the toxin and are less likely to be contaminated.