From the Waimakariri District Council – Published: 16-Jan-2019

The Community and Public Health division of the Canterbury District Health Board have issued health warnings for Ashley/Rakahuri River near the Rangiora-Loburn bridge and the Waimakariri River near the State Highway 1 and Main North Road bridges

These warnings come following algae being found in weekly testing carried out by Environment Canterbury (ECan).

For the latest information on where it’s safe to swim check the LAWA – Can I Swim Here?website before you go for a dip.

Waimakariri District Council’s Environment Services Manager, Malcolm Johnston, says the Council are installing warning signs in the two affected areas and people and animals should remain out of the waterways until the warnings have been lifted.

“We have closed these swimming sites for the safety of the community and  will let people know when it is safe to enter the water again. We appreciate the community’s understanding and encourage use of neighbouring swimming areas where there are no restrictions in place.”

Some algal blooms are ‘cyanobacterial blooms’, also known as ‘blue-green algae’ and their presence creates a need for water use restrictions.

Dr Ramon Pink, Canterbury Medical Officer of Health, says the algae look 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,” Dr Pink 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.”

He also warns that no one should drink from the river at any time, as even boiling the water will not remove the toxin and pets should be taken to a vet immediately if they are showing signs of illness after coming into contact with algal mats.

ECan monitoring sites weekly 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.