Health Warning – Algal Bloom in Ashburton River at SH1

The Community and Public Health division of Canterbury District Health Board are issuing a health warning after potentially toxic blue-green algae (benthic cyanobacteria) were found in the Ashburton River at SH1.

People and animals, particularly dogs, should avoid the area of the Ashburton River until further notice.

Dr Alistair Humphrey Canterbury Medical Officer of Health, says the algae look like dark brown to black mats and can produce toxins harmful to people and animals. As the algae mats are detaching from the riverbed and accumulating at the sides of the river there is increased potential for animals or humans to be in contact and therefore the public should be more vigilant.

“Exposure may cause skin rashes, nausea, stomach cramps, tingling and numbness around the mouth and fingertips,” Dr Humphrey says.

“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.”

Pets should be taken to a vet immediately if they are showing signs of illness after coming into contact with algal mats.

“Boiling the water from the river does not remove the toxin and so water from the river should not be consumed,” Dr Alistair Humphrey says.

People should avoid the affected area and animals should be kept away from 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.

Facts about cyanobacteria:

  • Appears as dark brown/black mats attached to rocks along the riverbed
  • The algae occur naturally but can increase rapidly during warmer months
  • It often has a strong musty smell and algal toxin concentrations can vary over short periods with changing environmental conditions
  • Although high river levels will remove the algal bloom, detached mats can accumulate along the shore and increase the risk of exposure to toxins.
  • If a health warning is in place avoid contact with the water
  • Although district or city councils may place warning signs, these may not be seen at the numerous river access points, hence the need for people/ dog-walkers to treat every low-flowing river cautiously.

For further information visit


View original article at: Health Warning – Algal Bloom in Ashburton River at SH1



Leave a Reply