Freshwater Harmful Algal Bloom-related Illness Tracking in California

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What are freshwater harmful algal bloom (HAB)-related illnesses?

When cyanobacteria (also known as blue-green algae) and algae in freshwater and estuarine waterbodies occur at levels that pose a risk to humans, animals, and the environment, they are referred to as freshwater harmful algal blooms (HABs). Humans and animals can become sick after ingesting or contacting cyanobacteria, water contaminated with cyanotoxins, or algal mats. Cyanotoxins may also accumulate in fish and shellfish. Signs and symptoms may occur within minutes or days following exposure and may include:

  • irritation of skin, ears, eyes, nose, or throat
  • abnormal breathing (coughing, wheezing, asthma-like symptoms)
  • vomiting, diarrhea, abdominal pain
  • headaches, agitation, weakness
  • seizures and death (in animals)

How can I report a HAB-related illness?

Please report any suspected HAB or potential HAB-related illness by any of these methods: 

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How can I protect myself, my family, and my pets from freshwater HAB-related illness?

Learn more on the
CA HABs Portal:

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Who is tracking HAB-related illnesses in California?

The Interagency HAB-related Illness Workgroup has investigated and tracked potential HAB-related illnesses in humans and animals throughout California. The workgroup includes staff from the Office of Environmental Health Hazard Assessment (OEHHA), the State Water Resources Control Board, the California Department of Public Health (CDPH), and the California Department of Fish and Wildlife (CDFW). All potential illness reports submitted to the workgroup undergo an evaluation of the available environmental and health-related information, and those considered HAB-related are included in final summaries (as noted below). Much of the information presented on this web page is also available as a one-page freshwater HAB illness tracking factsheet.

This workgroup also investigates and tracks marine HAB-related illnesses in California. For more information on marine HABs and how to report a potentially related human or animal illness, see OEHHA’s webpage on marine HAB-related illnesses.

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How many freshwater HAB-related illnesses have been reported for California?

From 2018 to 2021, CDPH reported 109 freshwater HAB-related human and animal illnesses for California to the Centers for Disease Control and Prevention (CDC) One Health Harmful Algal Bloom System (OHHABS). A summary of HAB-related illnesses reported by year is provided in the figure below. No livestock incidents have been reported to date.

HAB related illnesses reported in California 2018 through 2021

Figure 1. Freshwater illnesses reported as HAB-related to OHHABS from 2018 – 2021. Number represents individuals (except when submitted as group, such as fish).

In which counties did these reported freshwater HAB-related illnesses occur?

The maps below display the counties in which freshwater HAB-related illnesses for California (reported to OHHABS) have occurred for previously reported years combined (2018-2020) and for 2021. Illnesses are grouped by human-only, human and animal (domestic or wild), or animal only.


California map of HAB-related Illnesses

How are HAB-related illnesses being tracked across the United States?

The CDC’s OHHABS is a voluntary reporting system available to state and territorial public health departments and their designated environmental health or animal health partners. It collects data on individual human and animal cases of illnesses from HAB-associated exposures, as well as environmental data about HABs. OHHABS is an example of One Health surveillance. One Health is an approach that recognizes that human, animal, and environmental health are interconnected, and that human health, animal health, and environmental health communities can more effectively address many linked health challenges by working together.

For general information on HABs, please refer to the HABs FAQ webpage.