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World Health Organization (WHO) 1999 Guideline Values for Cyanobacteria in Freshwater

The World Health Organization (WHO) developed guidance values for the relative probability of acute health effects to account for the possible exposures through recreational activities (contact, ingestion and inhalation) during recreational exposure to cyanobacteria based on cyanobacterial cells and chlorophyll-a levels.

WHO’s Guidelines for Safe Practice in Managing Recreational Waters*

Guidance level or  situation How guidance level derived               Health risks             Typical actions
Relatively low probability of adverse health effects
20 000 cyanobacterial cells/ml
or
10 ug chlorophyll-a/litre with dominance of cyanobacteria
From human bathing epidemiological study Short-term adverse health outcomes, e.g., skin irritations, gastrointestinal illness Post on-site risk advisory signs
Inform relevant authorities
Moderate probability of adverse health effects
100 000 cyanobacterial cells/ml
or
50 ug chlorophyll-a/litre with dominance, of cyanobacteria
From provisional drinking-water guideline value for microcystin-LR and data concerning other cyanotoxins Potential for long-term illness with some cyanobacterial species health outcomes, e.g., skin irritations, gastrointestinal illness Watch for scums or conditions conducive to scums  and further investigate hazard
Post on-site risk advisory signs
Inform relevant authorities
High probability of adverse health effects
Cyanobacterial scum formation in areas where whole-body contact and/or risk of ingestion/aspiration occur.
Inference from oral animal lethal poisoning.
Actual human illness case histories
Potential for acute poisoning
Potential for long-term illness with cyanobacterial species Short-term adverse activities health outcomes, e.g., skin irritations, gastrointestinal illness
Immediate action to control contact with scums; possible prohibition of swimming and other water contact activities Public health follow-up investigation Inform public and relevant authorities

*Summarized by EPA from World Health Organization. 2003. Guidelines for safe recreational water environments. Volume 1, Coastal and fresh waters.

For more information on the WHO guidelines see: