SUBJECT:Health Warning – Algal Bloom in Selwyn River
Canterbury health authorities have issued a warning after potentially toxic blue-green algae (benthic cyanobacteria) was
found in the Selwyn River/Waikirikiri at Glentunnel camp site.
People should stay out of the water at this site until the health warnings have been lifted. Toxic algae are
particularly dangerous for dogs, so they should be kept away from the water.
Canterbury Medical Officer of Health Dr Alistair Humphrey 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. If you
experience any of these symptoms after contact with contaminated water, visit your doctor immediately,” he says.
No one should drink the water from the river at any time, Dr Humphrey says. Boiling the water does not remove the toxin.
However, tap water from the camp site itself is safe to drink because it is from the reticulated supply.
Animals should be taken to a vet immediately if they come into contact with the algal mats or if they display any
unusual symptoms.
Environment Canterbury is monitoring the site.
Environment Canterbury Senior Surface Water Quality Scientist David Kelly says that Phormidium cover of the stream bed at Glentunnel camp site is moderate to very high.
“Although our field staff did not observe Phormidium in the swimming hole at Glentunnel, mats are growing upstream and
downstream, and there is a risk that these will detach and be carried downstream,” Dr Kelly says.
“At the time of survey, there were no concerns with mat growths at the other Selwyn sites that we survey, such as
Whitecliffs and Coes Ford.”
Environment Canterbury monitors cyanobacteria weekly at the Selwyn River during summer and the public will be advised of
any changes in water quality that are of public health significance.
Facts about cyanobateria:
• The algae occur naturally but can increase rapidly during warmer months. It grows as dark brown/black mats
attached to rocks along the river, on the water surface, or on riverbanks.
• It often has a strong musty smell and algal concentrations can vary quickly with changing environmental
conditions.
• High river levels will remove the algal bloom.
• 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 http://ecan.govt.nz/services/online-services/monitoring/swimming-water-quality/Pages/river-warnings.aspx
Or contact Community and Public Health on (03) 364 1777.
ENDS