Can I swim here? If in doubt, keep out

With summer here, recreational water users are reminded to check the quality of Canterbury waterways.

Canterbury Medical Officer of Health Dr Alistair Humphrey said warnings remain in place where there are potentially toxic blue-green algae (cyanobacteria) in a number of areas.

"Make sure you check the health warnings for toxic algae before going near any waterways – and if in doubt, keep out,” Dr. Humphrey said.

Algal blooms can produce harmful toxins; people should avoid contact with the water where algal blooms are present until further notice. Algae is particularly dangerous for dogs.

What should I look out for?

"Animals showing signs of illness after coming into contact with toxic algae should be taken to a vet immediately. Symptoms of cyanotoxin poisoning in dogs include panting, lethargy, muscle tremors, twitching and convulsions – which usually occur within 30 minutes of exposure," Dr. Humphrey said.

"(In people) exposure may cause skin rashes, nausea, stomach cramps, tingling and numbness around the mouth and fingertips.

“If you experience any of these symptoms visit your doctor immediately and let them know you’ve had contact with the water,” Dr Humphrey said.

Can I drink water or eat fish from sites where a health warning is in place? 

People should never drink from a waterway where a health warning is in place and should avoid eating fish and shellfish taken from those areas.

Boiling the water does not remove the toxin.

What sites does Environment Canterbury monitor? 

Environment Canterbury Chief Scientist Dr. Tim Davie said it is not possible to monitor every stream and river in Canterbury.

"We monitor over 100 popular swimming sites in Canterbury; the results are updated weekly and shown on the Land Air Water Aotearoa (LAWA) website

"If you're swimming at non-monitored sites, we encourage you to check the stream bottom for what looks like black mats. If there are significant black mats, and if pieces are breaking off, you should not swim or allow dogs at the site," he said.

Keep in mind

  • Avoid cloudy, discoloured water, or water containing suspended globules
  • Stay away if there are black ‘mats’ covering the bottom of the waterway
  • Don’t swim after heavy rainfall or a weather event
  • Not all cyanobacteria blooms are visible. Avoid contact with the water if a health warning is in place

How to identify potentially toxic cyanobacteria

Check out what potentially toxic cyanobacteria (Phormidium) looks like so you can identify it and keep you, your family and pets safe this summer.