Health Warning – Algal Bloom in Ashley River at Loburn Bridge and Waipara River at Stringers Bridge

Friday January 13, 2012

Canterbury health authorities have issued a warning after ongoing water surveys of the Ashley and Waipara Rivers this week found high levels of potentially toxic algae (benthic cyanobacteria) at the Loburn Bridge on the Ashley River and at the Waipara River at Stringers Bridge.
Humans and animals, particularly dogs, should avoid the Ashley River/ Rakahuri at the Loburn Bridge and the Waipara River at Teviotdale and Stringers Bridges until the health warning has been lifted. 
Canterbury Medical Officer of Health Dr Daniel Williams says the algal mats can produce toxins harmful to humans and animals.
“Exposure may cause skin rashes, nausea, stomach cramps, tingling and numbness around the mouth and fingertips,” Dr Williams 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.”
Boiling the water from the river does not remove the toxin.
“No one should drink the water from the river at any time.”
However, reticulated town water supplies are currently safe.
Animals should be taken to a vet immediately if they come into contact with the contaminated rivers.
Environment Canterbury is monitoring the sites and the public will be advised of any changes in water quality.
A warning still remains in place for the Pareora River at Pareora Huts and Opihi River at State Highway 1 Bridge.
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

Or contact Community and Public Health on (03) 364 1777.​
Page last reviewed: 23 July 2013