Algal Bloom in Selwyn River

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