Cantabrians should check the status of local waterways for toxic algae (benthic cyanobacteria) this summer, following more health warnings issued for the region today.
The Community and Public Health division of the Canterbury District Health board have issued a health warning for the Ashley River/ Rakahuri at the Rangiora - Loburn Bridge
The warning comes after the latest Environment Canterbury monitoring results show there are increased concentrations of potentially toxic cyanobacteria in these waterways.
Dr Alistair Humphrey, Canterbury Medical Officer of Health, says people and animals should stay out of the river until the health warnings have been lifted.
The cyanobacteria at the Ashley River mostly comprises of Phormidium – a cyanobacteria which forms thick dark brown/black mats on the bed of the river.
“People and animals, particularly dogs, should avoid these waterways. Animals that show signs of illness after coming into contact with river water or Phormidium mats should be taken to a vet immediately.”
Reticulated town water supplies are currently safe but no one should drink the water from the river at any time , Dr Humphrey says.
“Boiling the water does not remove toxins. Symptoms from toxic exposure to the cyanobacteria range from rapid onset of nausea and diarrhoea, to gastroenteritis and other effects such as tingling and numbness around the mouth, fingertips, as well as liver damage,” Dr Humphrey says.
“If you experience any of these symptoms visit your doctor immediately and please let your doctor know if you have had contact with the river water.”
Fish can concentrate toxins and their consumption should be avoided. If fish are eaten, remove the gut and liver and wash in clean water.
Environment Canterbury monitors the river during summer and the public will be advised of any changes in water quality that are of public health significance.
Facts about cyanobacteria:
• It occurs naturally but can increase rapidly during warmer months.
• 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.
• It appears as dark brown/black mats attached to rocks along the riverbed.
• 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.