Harmful Algal Blooms (HABs):

Frequently Asked Questions

What are HABs and what are the problems?

Cyanobacteria (also known as blue-green algae) and algae occur in freshwater and estuarine waterbodies. Algae and cyanobacteria can produce harmful compounds, such as toxins and taste and odor compounds, that cause health risks to humans and animals. When blooms pose a risk to humans, animals, and the environment, they are referred to as harmful algal blooms (HABs).

 Cyanotoxins and algal toxins pose risks to the health and safety of people and pets, drinking water, and recreating in water bodies affected by blooms. They can also accumulate in fish and shellfish to levels posing threats to people and wildlife.  Sometimes the bloom is easily visible, forming a “scum” or discoloration on the water surface. Other times, it is less visible, floating beneath the surface or on the bottom of a water body (benthic).

 How do I detect HAB in the water?

Sometimes the bloom is easily visible, forming a “scum” or discoloration on the water surface. Other times, it is less visible, floating beneath the surface or on the bottom of a water body (benthic). Blooms can appear green, blue, yellow, red, or brown. Cyanotoxins, produced by cyanobacteria, cannot be visually detected in water or tissues.  Several guidance documents are available to aid identification of algae and cyanobacteria (Fact Sheet & Visual Guide), and the California Freshwater HAB Field Guide is available to assist in monitoring.

 What are the possible health concerns of HABs?

Cyanotoxins and algal toxins pose risks to the health and safety of people and pets, drinking water, and recreating in water bodies affected by blooms. They can also accumulate in fish and shellfish to levels posing threats to people and wildlife. Symptoms of HAB-related illness in people and animals are available from the Centers for Disease Control and Prevention (CDC), and by contacting the California Poison Control Center (1-800-222-1222).

Of the reported HAB-related incidents in 2017, there were 25 domestic animal deaths, numerous fish and wildlife, and 8 human incidents of illness.

What about animals and pets?

Pets, especially dogs, are susceptible to HABs because they swallow more water while swimming and playing in the water. They are also less deterred by green, smelly water that may contain HABs. Animals can experience symptoms within minutes of exposure to the toxins. These symptoms include vomiting, diarrhea, weakness, difficulty breathing, and seizures. In the worst cases, animals have died. If your pet experiences these symptoms after exposure, contact your veterinarian immediately. A veterinarian fact sheet and an outreach letter to veterinarians are available. For additional info refer to the Domestic Animals webpage.

What can I do?

Report any suspected HAB or potential HAB-related illness.

Practice Healthy Water Habits  at your local lake, river, or stream!

Where can I find info on marine HABs?

HABs occurring in marine (coastal) areas are outside of the scope of this Portal. Please refer to the Cal HAB Monitoring and Alert Program (CalHABMAP) that provides information on marine HABs. In addition, information on marine biotoxins in fish and shellfish are provided by CA Department of Public Health, OEHHA, and CA Department of Fish and Wildlife.