Blue-Green Algae: Health Concerns Related to Cyanobacterial Harmful Algal Blooms

There are many species of cyanobacteria in Wisconsin’s lakes and rivers. Only some species can produce cyanotoxins that make us sick. Others may not produce toxins at all or don’t make enough to cause a health concern. The types of toxins that cyanobacteria produce can target the liver, kidney, or nervous system. They also can irritate the skin.

Larger cyanobacterial blooms are more likely to have a higher concentration of toxin. There isn’t an easy, quick way to know if a bloom is harmful or not. It can take a lab several days to analyze a water sample for toxins. During that time, water conditions can change. Blooms can appear and disappear quickly, even within an hour, which makes it difficult for officials to decide when to close a beach.

Using a common-sense approach to blooms is the best way to stay safe. When you see a bloom, avoid the water (this includes pets, too).

View photos of blooms.

Common symptoms of cyanobacteria poisoning from cyanotoxins

Cyanotoxins can affect your health in different ways. Symptoms depend on:

• The type of toxin.
• How much of the toxin you were exposed to.
• How you were exposed (for instance, wading versus swallowing water by mistake while swimming).
• How long you were exposed.

Human symptoms

Common symptoms in humans include:

Symptoms in animals

Cyanotoxins can make animals very sick or even kill them. Animals can die within hours to days of swallowing these toxins.

Dogs are especially at risk of poisoning because of their behaviors, which can include:

• Drinking contaminated water
• Eating dead fish and other animals found near a bloom.
• Swimming in contaminated waters.
• Licking scum from their fur after swimming.

Cattle are at risk because their movements are often confined by fencing. They may be forced to drink from ponds that can have blooms.

Birds, fish, and other aquatic animals can also be affected by blooms. Learn more from the CDC (Centers for Disease Control and Prevention)—Illness and Symptoms: Cyanobacteria in Fresh Water.

Seek care from a vet immediately if your pets or livestock seem sick after going in or near water.

Common symptoms in animals include:

• Diarrhea
• Vomiting
• Excessive drooling
• Liver failure
• Seizures or convulsions
• Stumbling and falling
• Tiredness or weakness
• Trouble breathing
• Death within hours or days

If your pet enjoys swimming in lakes and rivers in Wisconsin, review Blue-Green Algae and Dog Safety, P-00089.

If you have questions about your pet or livestock, call either:

ASPCA Animal Poison Control Center at 888-426-4435

Pet Poison Helpline at 855-764-7661 

Note: There is a fee for these calls.

How to report a blue-green algae (cyanobacteria) illness

Members of the general public and veterinarians: should call 608-266-1120 or complete the Harmful Algae Bloom (HAB) Illness or Sighting Survey, F-02152 online form to report any blue-green algae blooms and related human or animal illnesses.