Monitoring has identified relatively high cover of potentially toxic cyanobacteria algae in the Opihi River at Salesyard Bridge near Pleasant Point.
Community and Public Health have therefore issued a health warning and signage will be erected at that site. Once monitoring indicates that the river is safe, the signs will be removed.
Warnings remains in place at:
Opihi River at SH1Saltwater Creek at Coonoor Road
Humans and animals, particularly dogs, should avoid these areas until the health warning has been lifted.
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", as boiling the water from the river does not remove the toxin.
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.
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.
Further information on cyanobacteria is available from ECAN:
For more information on health effects, contact Community and Public Health on (03) 687 2600.
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