Cyanobacteria Harmful Algal Blooms (HABs) and Cyanotoxins in Recreational Waters

Cyanobacteria (also known as blue-green algae) are non-pathogenic, photosynthetic bacteria that commonly grow in outdoor waters. Cyanobacteria can quickly multiply into a harmful algal bloom (HAB) in the right environmental conditions. Many cyanobacteria can produce toxins, cyanobacteria bloom in a riverwhich are collectively referred to as cyanotoxins. Several cyanotoxins are extremely toxic to laboratory animals and have poisoned people. People swimming, waterskiing, or boating in these water bodies can be exposed to cyanotoxins by inadvertently swallowing water or inhaling aerosols. Skin contact can lead to irritation and rashes. People exposed to cyanotoxins in recreational waters may experience eye irritation, skin irritation or rash, vomiting, diarrhea, and cold and flu-like symptoms. Ongoing daily exposures can lead to more serious effects. Dogs playing in or near recreational waters have died after drinking scummy water or eating algae with high levels of cyanotoxins.

OEHHA evaluated the potential health risks from three cyanotoxins commonly found in California: microcystins, anatoxin-a, and cylindrospermopsin. OEHHA identified Action Levels* (levels of toxin in recreational water, algal mats, and fish filets that justify regulatory actions needed to protect public health). Cyanotoxin concentrations at or below these Action Levels are not expected to lead to adverse health effects. When toxins are found at concentrations above the Action Levels, a public health response is recommended, such as continued monitoring or issuance of public health notices. OEHHA worked with the California Cyanobacteria and Harmful Algal Bloom (CCHAB) Network to incorporate these Action Levels into a multi-tier response plan for cyanotoxins in recreational waters. The CCHAB multi-tier response plan is available in the 2016 updates to the Statewide Voluntary Guidance.

*These Action Levels are provided as guidance and are not regulatory.


Please contact Regina Linville if you have any questions