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Algae and cyanobacteria are an essential part of aquatic ecosystems, but at times they can produce biotoxins that pose a health hazard for humans and animals. When potentially hazardous algae or cyanobacteria grow too fast or bloom, they are termed harmful algal blooms (HABs).
Symptoms associated with exposure to HABs include dermal, eye, ear, and allergy symptoms from direct contact with contaminated water or from touching algal mats. Respiratory, nose, and throat symptoms can be associated with inhalation of contaminated water spray or aerosolised toxins. Vomiting and diarrhoea are common following recreational water cyanotoxin exposure.
Swallowing contaminated water containing high concentrations of HAB species could cause neurological, gastroenterological, and liver symptoms.
It is likely that the risks from HABs will increase as the impacts of climate change result in lower river flows and increased water temperatures.
Cases of biotoxin poisoning from HABs must be notified to the Medical Officer of Health as they are classified as poisoning arising from chemical contamination of the environment under Schedule 2 of the Health Act 1956.
The guidelines provide advice to public health officers on the environmental case management of people who may have been exposed to harmful algae or cyanobacteria in recreational water in New Zealand.
The 2026 revisions are minor and administrative only. They include the updated WorkSafe notification form in Appendix D. This form is to be used when medical officers of health notify WorkSafe of work-related notifiable diseases or hazardous substances injuries under section 199 of the Health and Safety and Work Act 2015. Links to other publications have also been updated.