From Health New Zealand

Health New Zealand/Te Whatu Ora has lifted its algal bloom health warning issued for Lake Hood on 20/03/2025.

Recent water testing at Lake Hood has shown the quantity of potentially toxic blue-green algae (planktonic cyanobacteria) in the lake has reduced and concentrations are now below levels that are of concern to public health.

Dr Ramon Pink, Medical Officer of Health for the National Public Health Service, says Environment Canterbury’s sampling of Lake Hood will continue on a monthly basis.

“The public will be informed if testing shows that concentrations have increased and there is a risk to public health again”, Dr Pink says.

Facts about cyanobacteria

• The algae occur naturally but can increase rapidly during warmer months.
• Algal blooms are caused by a combination of nutrients in the water (such as nitrogen and phosphorus), and favourable weather conditions (e.g., increased temperature, calm days).
• If the water is cloudy, discoloured, or has small globules suspended in it, avoid all contact.
• Not all cyanobacterial blooms are visible to the naked eye and toxins can persist after the blooms disappear.
• Cyanobacterial concentrations can change quickly with changing environmental conditions (e.g., wind). If a health warning is in place avoid contact with the water.
• If a warning is in place, people and animals should not drink the water from the lake at any time, even boiled water.
• Exposure to an algal bloom can cause skin rashes, nausea, stomach cramps, tingling and numbness around the mouth and fingertips. If you experience any of these symptoms visit your doctor immediately and please let your doctor know if you have had contact with lake water when there is a health warning in place.

For further details visit: lawa.org.nz/explore-data/canterbury-region/

Or contact Te Mana Ora | Community and Public Health on (03) 364 1777:
cph.co.nz/your-health/recreational-water/

For more information about Mahinga Kai:
cph.co.nz/wp-content/uploads/saf0112.pdf