Media release from South Canterbury DHB

The South Canterbury Medical Officer of Health has issued a warning after water surveys of the Pareora and Opihi Rivers this week found moderate levels of the potentially toxic blue-green algae (benthic cyanobacteria), with algae accumulating along the river edges.

Humans and animals, particularly dogs, should avoid the Pareora River at Pareora Huts, and the Opihi River at Waipopo, until the health warnings have been lifted.   

South Canterbury Medical Officer of Health Daniel Williams says the algal mats can produce toxins harmful to humans and animals. The risk of exposure to toxins is increased when algal mats break off and accumulate as scum along the river edge.  

"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.

Drinking contaminated water, even boiled water, from these rivers should be avoided at all times, Dr Williams says.

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.

Facts about cyanobacteria:

The algae occur naturally but can increase rapidly during warmer weather and low river flows. It grows as dark brown/black mats attached to rocks along the river, and may detach and accumulate along riverbanks.  
It often has a strong musty smell and algal concentrations can vary quickly with changing environmental conditions.
Although high river levels will remove the algal bloom, mats often accumulate onshore immediately after increased flows.
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