Health Risks Associated with HABs

Many species of blue-green algae produce chemical compounds that are toxic to warm-blooded creatures (people, pets, livestock, and wildlife), and some are toxic to other organisms like fish. The biggest risk to health comes from contact with or ingestion of the toxins produced by the blue-green algae bloom during activities that bring an individual into full-body contact with the water (during swimming, skiing or jet skiing, for example), or from inhaling spray cast up from the water's surface, either by recreational activities or by the wind.

Children and pets are most at risk while engaging in recreation in the water because they are more likely to accidentally or intentionally swallow lake water. Pets can become ill after being exposed to spray. They can also become ill from eating dried algae along the shore or after licking affected water or algae from their fur. It is best to keep pets and children far away from exposure and move to safer locations. Adults with compromised immune systems are also more susceptible to illness from exposure.

These toxins can affect the liver, nervous system, skin, and other organs. The most common complaints after recreational exposure include vomiting, diarrhea, skin rashes, eye irritation, and respiratory symptoms. Blue-green algae (toxic and non-toxic varieties) can also cause dermatological symptoms from prolonged skin contact with water or wet clothes. Some algal toxins are quite toxic and fast-acting. Exposure to algal toxins can cause illness or possibly even death. No antidotes exist for any known algal toxins, and the compounds are not destroyed by boiling. This makes prevention the best option for protecting human and animal health during a bloom.

When in doubt, stay out

The following figure shows some of the potential symptoms from exposure to Harmful Algal Blooms (HABs).

Route of Exposure

Signs & Symptoms

Time to Symptom Onset

Differential Diagnosis

Hepatotoxins: Swallowing water contaminated with cyanobacteria or toxins

Elevated ALT
Acute hepatitis
Kidney Toxicity

Minutes to hours

Other hepatotoxin poisonings, other microbial infections/toxins

Neurotoxins: Swallowing water contaminated with cyanobacteria or toxins

Motor weakness
Respiratory paralysis

Minutes to hours

Pesticide poisoning, other toxic poisonings

Dermatotoxins: Skin contact with water contaminated with cyanobacteria or toxins or contact with animals

Itchy skin
Red skin
Skin blistering
Allergic reaction

Minutes to hours

Other dermal allergens, non-allergic urticaria, photosensitivity reactions

Inhaling aerosolized droplets contaminated with cyanobacteria or toxins

Sore throat
Upper respiratory irritation
possible allergic reaction

Unknown, but likely an acute reaction

Other airborne allergens, upper respiratory infection, flu

More information

See also the KDHE article, "Human Illnesses and Animal Deaths Associated with Freshwater Harmful Algal Blooms in Kansas" (PDF). For scientific research related to Harmful Algal Blooms and Health, see this special edition of the journal Toxins: "Harmful Algal Blooms (HABs) and Public Health: Progress and Current Challenges."

Additional Resources