Symptoms of Illnesses Caused by Harmful Algal Blooms

Key points

  • Harmful algal blooms can cause mild to life-threatening illnesses.
  • Symptoms depend on the type of harmful algal bloom you come in contact with.
  • Animals—including pets, livestock, and wildlife—can get very sick and die from contact with harmful algal blooms.
Young woman with her face contorted in pain lying on a couch with one hand on her forehead and the other on her stomach

Early symptoms

Harmful algal blooms that grow in lakes or rivers often cause different symptoms than those in oceans or bays.

Symptoms depend on:

  • How you are exposed (come into contact with harmful algal blooms or the toxins they make)
  • How long you are exposed
  • Which type of toxin is present
  • How much toxin is present
River with bright green, streaky water on the left and sea with bright pink, streaky water on the right.
Harmful algal blooms in fresh water (left photo) often cause different symptoms than those in salt water (right photo).

Common symptoms include:

  • Stomach pain
  • Rash
  • Headache
  • Coughing
  • Watery eyes
  • Nose irritation
  • Sore throat

These symptoms are most often caused by having contact with water or food containing harmful algae, cyanobacteria (blue-green algae), or their toxins. Contact includes touching water, breathing in tiny water droplets, or swallowing water or food.

More serious symptoms can include:

  • Liver damage
  • Seizure
  • Irregular heartbeat

Serious illnesses are most often caused by eating seafood or swallowing water containing certain harmful algal bloom toxins.

Keep Reading: Symptoms Caused by Freshwater Harmful Algal Blooms
Keep Reading: Symptoms Caused by Saltwater Harmful Algal Blooms

Later symptoms

The long-term health effects of harmful algal blooms for people and animals remain unclear. Researchers are still learning about these effects.

When to talk to your doctor

If you think you have symptoms caused by a harmful algal bloom, contact a healthcare provider. They can give you advice about how to relieve your symptoms.

You can also call the Poison Control hotline at 1-800-222-1222. The specialists might be able to give you information about illnesses caused by harmful algal blooms.

Reporting helps prevent additional illnesses‎

Report illnesses that you believe were caused by a harmful algal bloom to your local or state health department. This helps them understand and prevent future illnesses. Some state health departments have forms on their websites or hotlines for reporting these illnesses.
Find your health department

Signs and symptoms in animals

Animals—including pets, livestock, and wildlife—can get very sick and die from contact with harmful algal blooms.

Signs of illness in animals can include:

  • Throwing up
  • Loss of energy
  • Stumbling and falling
  • Seizures

Call a veterinarian right away if your animal shows any of these signs. Animals can get sick and die within hours of swallowing harmful algal bloom toxins in water, food, or algae.

Keep Reading: Preventing Pet and Livestock Illnesses Caused by Harmful Algal Blooms

Resources

Food Poisoning from Marine Toxins | CDC Yellow Book

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Content Source:
National Center for Emerging and Zoonotic Infectious Diseases (NCEZID); National Center for Environmental Health