Protect Yourself and Your Pets

Man with dog at the edge of a small river

It is not possible to know if a large growth, or bloom, of algae or cyanobacteria (also called blue-green algae) is harmful just by looking at it. Some blooms make toxins (poisons), which can still be in the water even when you can’t see a bloom. Learn how to protect yourself and your loved ones from harmful algae and cyanobacteria, what to do if you or a pet is exposed to them, and how to help prevent these blooms.

Recreational water

Check for advisories before visiting a body of water

health advisory sign

Permanent harmful cyanobacterial bloom health advisory sign in Oregon. Photo courtesy of Oregon Public Health.

Check for local and state swimming or fishing advisories before visiting lakes, rivers, and oceans. Follow advisories to reduce your chances of getting sick.

Health or environmental protection departments often post advisories on their websites, near the water, or both. The Environmental Protection Agency (EPA) also has a list of many state monitoring programs.

Visit your state government website to find out more information about water testing and beach closures in your area. Some states provide information on state laboratory testing as well as other environmental and health information.

Stay out of water with a bloom

If you see signs of a bloom, stay out of the water and keep your pets out of the water. You cannot tell if a bloom is harmful by looking at it, so it is best to use caution and stay away. Do not fish, swim, boat, or play water sports in areas where this is possible harmful algae or cyanobacteria.

Do not go into or play in water that:

  • Smells bad
  • Looks discolored
  • Has foam, scum, algal mats, or paint-like streaks on the surface
  • Has dead fish or other animals washed up on its shore or beach

Protect your pets and livestock from getting sick by keeping them away from water with possible harmful algae or cyanobacteria. Do not let animals:

  • Get in the water
  • Drink the water
  • Lick or eat mats of cyanobacteria or algae
  • Eat or graze near the water
  • Eat dead fish or other animals on the shore
  • Go on the beach or shoreline

Learn more about protecting your animals from harmful cyanobacteria (blue-green algae).

Developed algae at the surface of a slow flow freshwater lake

Harmful algae and cyanobacteria can make the water look or smell bad. When in doubt, it’s best to keep out!

Rinse off if you or your pets go in water

If you or your pets do go in water that may have a bloom, rinse yourself and your pets immediately afterward with tap water from a sink, shower, hose, or outdoor spigot. Do not let pets lick their fur until they have been rinsed. Pets may have harmful algae, cyanobacteria, or related toxins on their fur if they swim or play in water with a bloom.

Do not fill pools with water directly from lakes, rivers, or ponds. The water could contain algal or cyanobacterial toxins or unsafe levels of germs.

Drinking water

Pot with boiling water

Don’t boil water contaminated with toxins. Boiling water does not remove toxins and can concentrate the toxin.

Follow local guidance about toxins in tap water

If you are notified of cyanobacteria or their toxins in your public drinking water supply, follow guidance from your local or state government or water utility to reduce the chances of you or your animals getting sick.

Harmful cyanobacteria may grow in water bodies that supply tap water. Although many water treatment plants can remove these toxins, tap water can be contaminated in certain situations. Cyanobacteria can also produce substances that are not harmful, but can change the taste or smell of tap water.

If you have concerns about the appearance, smell, or taste of tap water that you are using, contact your water utility or health department. Consider using bottled water for drinking and cooking until the problem is resolved.

Report possible harmful algae and cyanobacteria

If you are worried about the way recreational water looks or smells, contact your local park authority, environmental protection authority, state environmental protection department, or health department. If you are worried about the way your tap water looks, smells, or tastes, contact your water utility or health department.

If you would like to help track harmful algae and cyanobacteria, check to see if your state has a citizen science program. For example, some states use tools like the BloomWatch app, the CyAN app, or the National Phytoplankton Monitoring Network. Examples of state-specific citizen science programs include:

Young woman sitting on a couch feeling ill

Report any illnesses that you think were caused by a bloom or its toxins to your local or state health department.

Fish and shellfish

Be aware of advisories and health risks related to eating contaminated fish and shellfish

Avoid eating very large reef fish (such as grouper or amberjack), especially the head, gut, liver, or roe (eggs). Large reef fish may be contaminated with ciguatoxin, the algal toxin that causes ciguatera fish poisoning. See the U.S. Food and Drug Administration’s (FDA) Fish and Fishery Products Hazards and Controls Guidance for more information on reef fish associated with unsafe levels of toxins.

Check for and follow local shellfish and fish advisories before eating any fish or shellfish you collect yourself. Algal and cyanobacterial toxins in fish or shellfish have no taste or odor. Cooking or preserving food does not remove toxins. Thus, you cannot tell if the seafood is safe by just looking at, smelling, or tasting it.

  • Check to see if shellfish beds are closed. State shellfish control authorities (usually state health departments or other state agencies) are required to control for toxins where harmful algal blooms are likely to occur and toxins could build up in shellfish. Common ways state authorities control for algal toxins include routine monitoring for toxic algae or shellfish and testing shellfish for toxins before or after harvesting. If levels of toxins are unsafe, state authorities will close the area for shellfish harvesting until shellfish are safe to eat.
  • Check safety advisories from the Environmental Protection Agency’s (EPA) Fish and Shellfish Advisories and Safe Eating Guidelines website.

What to do if you have symptoms

If you think you may have symptoms caused by harmful algae, cyanobacteria, or their toxins, you can:

  • Talk to your healthcare provider for advice about how to relieve your symptoms. Let them know that you might have recently come in contact with a bloom or its toxins. While there are currently no available tests or special treatments for illnesses caused by algal or cyanobacterial toxins, information about the suspected cause of your illness might help your healthcare provider manage your symptoms.
  • Call your poison control center hotline at 1-800-222-1222. The specialists can provide information about illnesses caused by blooms.
  • Report any illnesses that you believe were caused by algae, cyanobacteria, or their toxins to your local or state health department. This information can help them understand and prevent harmful blooms and illnesses. Some state health departments have forms on their websites or hotlines for reporting suspected bloom-associated illnesses.

For more information about symptoms, visit Illness and Symptoms.

If you think your animal has been exposed to harmful algae, cyanobacteria, or their toxins, you should:

  • Rinse them with tap water right away to prevent them from licking algae or cyanobacteria off their fur.
  • Call your veterinarian right away if you think your pets or livestock swallowed water with a bloom, licked harmful algae or cyanobacteria off their fur, or ate fish or other creatures killed by a harmful algal bloom.
  • Call an animal poison center. You can call the ASPCA Animal Poison Control Center at 1-888-426-4435 or the Pet Poison Helpline at 1-855-764-7661 if you have questions about your pets or livestock. (Note: there is a fee for these calls.)
  • Report any illnesses that you think were caused by algae, cyanobacteria, or their toxins to your local or state health department.

While no human deaths caused by cyanobacteria have been reported in the United States, many dog deaths have been reported after dogs swam in or drank fresh water containing cyanobacterial toxins. For dogs and other animals, some cyanobacterial toxins can cause illness or death in hours to days.

Prevent harmful algal and cyanobacterial blooms from forming

Use only the recommended amount of fertilizers on your farm, yard, and garden. This will reduce the amount of nutrients running off into nearby water bodies. Nutrients in the water can help algae and cyanobacteria to grow more quickly than usual.

Maintain your septic system to keep wastewater from leaking and seeping into nearby bodies of water. Wastewater is full of nutrients that can feed algae and cyanobacteria.

Learn more about factors that can help harmful algae and cyanobacteria grow.

Page last reviewed: September 20, 2022