SCDHB

Community and Public Health have issued a new warning after water surveys of the Opihi River have found high levels of potentially toxic dark brown/black algae (Phormidium) at Saleyards Bridge. These algal mats are now detaching and may accumulate along the edge of the river.

The current warnings, issued in December for the Opihi River at State Highway One, and the Pareora River at the Huts, are still in effect.

Humans and animals, particularly dogs, should avoid all these river areas until the health warning has been lifted. 

South Canterbury Medical Officer of Health Dr Daniel Williams 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," Dr Williams 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."

"No one should drink the water from the river at any time."

Boiling the water from the river does not remove the toxin. However, reticulated town water supplies are currently safe.

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:

• 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.

Contact Community and Public Health on (03) 687 2600.