Issued: 22 May 2026
Caution advised – Cyanobacteria scums may be present.
Potentially toxic cyanobacteria scums have been observed for Lake Opuha above the dam. Please avoid direct contact with these green coloured surface scums.
Facts about cyanobacteria
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Cyanobacteria occur naturally but can increase rapidly during warmer months.
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Harmful algal blooms are caused by a combination of nutrients in the water (such as nitrogen and phosphorus), and favourable weather conditions (for example as increased temperature, calm days).
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If the water is cloudy, discoloured, or has small globules suspended in it, avoid all contact.
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Not all cyanobacterial blooms are visible to the naked eye and toxins can persist after the blooms disappear.
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Cyanobacterial concentrations can change quickly with changing environmental conditions (e.g., wind). If a health warning is in place avoid contact with the water.
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Animals that show signs of illness after coming into contact with algal scums should be taken to a vet immediately.
For further details visit:
https://www.lawa.org.nz/explore-data/canterbury-region
To contact your local National Public Health Service office visit:
https://info.health.nz/locations/canterbury/national-public-health-service-canterbury-west-coast