Toxic Algae (Cyanobacteria)

Current Toxic Algae and Surface Water Advisories

Toxic Algae

Toxic algae, also known as cyanobacteria or blue-green algae, can produce toxins. These toxins may kill pets, waterfowl, and other animals. They can also cause serious illness or even death in people. Toxic algae are naturally occurring and could have increased in number because of impacts from human activities.

What is a Toxic Algae Bloom?

Toxic algae can reproduce rapidly in fresh water when the amount of sunlight, temperature and nutrients are sufficient. Within a few days a "clear" lake, pond or ditch can become discolored with algae growth. A bloom forms when a sudden increase in the concentration of algae cells happens in a certain area of water. Toxic algae blooms often float to the surface and can form a surface scum. This scum, or heavy concentration of algae, can look like green paint and be several inches thick near the shoreline (click here for an example). Wind and weather conditions can greatly change the amount and location of algae.

What are the symptoms?

If someone swallows water with toxic algae, they may experience:

  • Muscle weakness.
  • Vomiting.
  • Diarrhea.
  • Nausea.

If you know or believe someone may have swallowed water containing large amounts of algae, it is extremely important to seek medical attention.

Skin contact with toxic algae can cause irritation or a rash. This rash is different than the one caused by Swimmer's Itch.

How can toxic algae affect my pets?

The risk to pets is much greater than it is to people. Pets have smaller body sizes, are more likely to drink water containing a large amount of algae, and may groom by licking their fur after contact with water containing toxic algae. Pets and other animals may show these symptoms if they ingest toxic algae:

  • Lethargy.
  • Vomiting.
  • Diarrhea.
  • Convulsions.
  • Difficulty breathing.
  • General weakness.

What you should I do if I’m exposed to toxic algae?

The onset of illness can happen within minutes to hours of exposure. You should rinse off anyone or any pets exposed to toxic algae immediately. Monitor for signs of illness and seek medical treatment if symptoms occur. For exposed pets, keep them from licking their fur to groom.

Can I eat fish from toxic algae contaminated water?

Avoid eating fish from areas with visible algae. Always clean fish well and discard guts.

What should I do if I see an algae bloom?

Follow these steps to keep yourself, your family, and your pets safe:

  • Tell us! Get involved with our Algae Watch Volunteer Group. Email to sign up. 
  • Do not drink lake water.
  • Do not swim or water ski in areas with visible algae (looks like paint on the surface).
  • Keep pets and livestock away.
  • If the area is open to the public and isn’t already posted with a Health Department sign, please call us at (253) 798-6470.

What can I do about it?

Algae need nutrients—like phosphorous and nitrogen—to grow. These nutrients are found in animal and human waste (sewage) and fertilizers. Here’s what you can do to prevent toxic algae:

  • Eliminate or reduce use of fertilizers.
  • Properly use and maintain your septic system. Have your system inspected every one to three years and pumped as needed. For more information, visit
  • Keep animal waste out of streams or lakes! Pick up after your pets, don’t feed waterfowl, and keep livestock away from the water.
  • Plant native plants between your yard and the creek or lake to reduce runoff and prevent erosion.

Find out more!

We've added a new link to the CDC website under our related links section. Check it out!

Toxic Algae Advisory Explanations

  • Caution Advisory (Posted Sign): Lake may be unsafe for people and pets.
  • Warning Advisory (Posted Sign): Lake is unsafe for people and pets.

For more information, or to report a suspected algae bloom, please call the Health Department at (253) 798-6470 or email us at


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