Health Warning - Algal Bloom in Kahutara River near SH1

Thursday December 4, 2014

‚ÄčThe Community and Public Health division of the Canterbury District Health Board have issued a health warning for Kahutara River near State Highway 1, Peketa.

Dr Alistair Humphrey, Canterbury Medical Officer of Health, says people and animals should avoid the river near State Highway 1 and the lagoon after potentially toxic blue-green algae (benthic cyanobacteria) was found.

The Phormidium  (benthic cyanobacteria) extends from the main stem of the river down into the lagoon south of the Peketa camping ground.

"The mats are detaching and will be accumulating in the lagoon, so I would advise that the lagoon be avoided," Dr Humphrey says.

"The benthic mats may also extend further upstream and river users should keep an eye out for dark brown or black mats which can produce toxins harmful to people and animals."

Dr Humphrey says 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."

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

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

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

Dr Humphrey says 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.

  • Cyanobacteria 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

Or contact Community and Public Health on (03) 364 1777.


For more information contact Canterbury DHB Media Advisor Amy Milne on (03) 364 4122, 027 5027523, or

Page last reviewed: 04 December 2014