| 08 Mar 2024

Health Warning – Opihi River Catchment

Health New Zealand | Te Whatu Ora has issued a health warning for the entire Opihi River Catchment.

The warning follows finding moderate to high cover of toxic algae (benthic cyanobacteria) at multiple sites across the entire Opihi River Catchment.

People should avoid the area and animals, particularly dogs, should not be allowed near the water until the health warning has been lifted.

All access points along the entire Opihi River may have benthic cyanobacteria present. People are advised to treat every low-flowing river cautiously, check for the presence of benthic cyanobacteria and avoid contact.

Dr Matthew Reid, Medical Officer of Health for the National Public Health Service, says the algae looks like dark brown to black mats and can produce toxins harmful to people and animals.

“Exposure may 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, also let your doctor know if you’ve had contact with dark brown/black algal mats or water in this area”, Dr Reid says.

Pets that show signs of illness after coming into contact with algal mats should be taken to a vet immediately.

People and animals should remain out of the waterways until the warnings have been lifted.

Environment Canterbury is monitoring the sites and the public will be advised of any changes in water quality.

Sites that are currently under a temporary health warning in South Canterbury include:

  • Pareora River/Pureora at SH1 Bridge
  • Hae Hae Te Moana River at Gorge
  • Waihao River at Bradshaws Bridge
  • Opihi River at SH79 Bridge
  • Opihi River at SH1
  • Opihi River at Grassy Banks
  • Opihi River at Saleyards Bridge
  • Opihi River at Raincliff Bridge
  • Temuka River at Manse Bridge
  • Temuka River at SH1 Bridge
  • Saltwater Creek/Otipua at SH1 Bridge.

Facts about cyanobacteria
  • Cyanobacteria 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.

For further details visit:

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

For more information about Mahinga Kai:



For further information, contact:

Karen Berry
Public Health Communications Lead
National Public Health Service
Te Waipounamu
Health NZ  
021 139 7442