Harmful Algal Blooms (HABs)

OEHHA performs risk assessment and hazard evaluation activities relating to Harmful Algal Blooms (HABs) in lakes, rivers, and ocean environments. An algal bloom is a rapid growth of algae and/or cyanobacteria (also known as blue-green algae) in water. An algal bloom is harmful when the algae or cyanobacteria produce toxins that can adversely impact humans, wildlife, or domestic animals. Non-toxic algal blooms are harmful when they adversely impact the aquatic ecosystem through crowding out other species, depleting dissolved oxygen, or disrupting other ecological factors.

OEHHA’s work focuses on the toxic impacts of HABs on humans and animals. Marine HABs commonly consist of an overgrowth of certain types of algae (diatoms or dinoflagellates) that produce biotoxins. HABs commonly found in California freshwater and estuarine environments are a type of photosynthetic bacteria (cyanobacteria) that can produce cyanotoxins. Factors promoting HABs include warmer temperatures and excess nutrients. Currently, OEHHA’s work on HAB-related toxins focuses on consumption of contaminated seafood, exposure during swimming and other recreational water activities, and their impacts on the health and well-being of humans, domestic animals, fish and invertebrates, and wildlife.

OEHHA’s work relating to HABs includes:

Marine HABs

• Marine biotoxin (domoic acid) in fish and shellfish
• Marine HAB-related illness tracking

Freshwater and Estuarine HABs

• See what HABs look like (pdf)
• Learn what you can do to protect yourself
• Cyanotoxins in recreational waters
• Freshwater and estuarine HAB-related illness tracking (CA HABs Portal)
• May 6, 2021 Notice of Availability of Notification Level Recommendations for Four Cyanotoxins in Drinking Water
• Jun 16, 2022 Notice of Availability of Acute Notification Level Recommendations for Four Cyanotoxins in Drinking Water