Cyanobacteria, also known as blue-green algae or harmful algal blooms, are tiny organisms commonly found on land and in lakes, rivers, ponds, estuaries, and marine water.
Cyanobacteria Bloom
A combination of warm temperatures, sunlight, and nutrient-rich waters can cause cyanobacteria to reproduce rapidly. Within a few days, a clear lake, pond, or ditch can become cloudy with algae growth, which is called a "bloom." These blooms usually float to the surface and can be several inches thick near the shoreline.
Although cyanobacteria can be a nuisance and cause poor water quality, most are not toxic. A cyanobacteria bloom:
- Often looks like green paint floating on the water, but it can also look bluish, brownish, or reddish green.
- Is made up of extremely small organisms that cannot be identified by eye.
- Is most common in the summer and fall, but it can form anytime.
Toxic Bloom
Some cyanobacteria produce toxins or poisons called cyanotoxins. These cyanotoxins can cause illness in humans, pets, waterfowl, and other animals that come in contact with the algae. In severe cases, toxic blooms can kill livestock and pets that drink the water. Eventually, the toxins break down in the water and are destroyed naturally.
Signs of a toxic bloom include:
- Dead fish, waterfowl, or other animals.
- Sudden, unexplained sickness or death of a cat or dog, especially if it has algae on its mouth, legs, or feet.
- Skin rashes on humans after being in the water.
How the Toxins Affect Animals and People
Cyanobacteria can produce nerve toxins (neurotoxins) and liver toxins (hepatotoxins). Call your doctor or veterinarian right away if you or your pets or livestock have signs of poisoning.
Drinking water is sometimes taken from surface water sources (such as reservoirs) that can have algal blooms. If there is a bloom, do not drink the water until laboratory testing shows the water is safe.
Neurotoxin (Nerve) Poisoning
- In people, signs include numbness of the lips, tingling in fingers and toes, and dizziness.
- In animals, signs include weakness, staggering, difficulty breathing, convulsions, and death.
- Signs appear within 15–20 minutes after ingestion.
Hepatotoxin (Liver) Poisoning
- Signs include abdominal pain, diarrhea, and vomiting in humans and death in animals.
- It may be hours or days before signs of liver poisoning appear.
If You See a Bloom
- When in doubt, stay out!
- Avoid all contact with water containing algae.
- Keep pets and livestock away from the water.
- Contact the environmental health section of your local health department or the Department of Ecology's Freshwater Algae Control Program.
- Learn how to report and test an algae bloom to confirm whether or not a bloom is toxic.
How to Get a Lake Sample Tested
If you think your lake has an algae bloom, go to Washington State Toxic Algae, Report and Test a Bloom for help identifying the algae and conducting a toxin analysis.
If a Test Confirms a Toxic Bloom
If a test shows that a bloom is toxic, county health officials will decide whether to close the lake for recreation, post notifications, or wait for further testing.
Limitations of Testing
Testing in one area of a lake doesn't ensure all areas of the lake are safe from a toxic bloom. Cyanobacteria blooms are known to be very patchy. There may be higher levels in areas not surveyed, particularly along shorelines. People and pets should avoid contact with lake water that clearly contains algae or has a green to blue-green color.
How We Determined When the Water is Safe
The Washington State Department of Health recommends testing the water once a week after toxin levels are identified as too high. Recreational use should be avoided until levels drop below recommended guidelines. Local health officials will decide when to reopen an area.
Eating Fish
Toxins can accumulate in fish tissues, especially in the liver, kidneys, and other organs. Be cautious about eating fish caught in areas where major cyanobacteria blooms occur. Before eating, remove the fish’s internal organs, which might contain more of the toxin.
How You Can Help
- Learn how to identify and report blooms.
- Caution others to avoid water when blooms occur and keep pets and livestock away.
- Report algae blooms to your local health department or Department of Ecology's Freshwater Algae Control Program.
- Limit the use of fertilizers. These contain nitrogen and phosphorus that find their way to lakes and streams and contribute to blooms. Phosphorus is known to contribute to algae growth. RCW 15.54.500, Turf fertilizer - Prohibitions on application, sales, and retail display discourages homeowners from using fertilizers with phosphorus on healthy lawns.
More Resources
Harmful Algal Bloom Resources - Communication materials, guidance documents, and contacts.
Cyanobacteria Technical Information - Specific cyanobacteria species and associated toxins.