Toxic algae 

Known also as cyanobacteria, toxic algae are naturally occurring, often blooming in warm, summertime conditions in lakes and rivers. 

Toxic algae can be harmful to humans, and is especially dangerous to animals, such as dogs.

Please take care if walking your dog near any waterways. Keep them away from anything that resembles toxic algae.

Don’t go swimming in areas with toxic algae present.

Check for toxic algae warnings in your area.

Known toxic algae hotspots in Otago

Rivers:
  • Silver Stream, Mosgiel
  • Cardrona River, Queenstown-Lakes
  • Manuherekia River, Central Otago
  • Hāwea River, Queenstown-Lakes
  • Waianakarua River, North Otago
Lakes:
  • Lake Waihola, Clutha
  • Tomahawk Lagoon, Dunedin
  • Butchers Dam, Central Otago


How to spot toxic algae

In lakes it gives the water a murky green appearance like pea soup. 

In rivers it looks like dark brown tar mats on the riverbed and banks that can have a strong musty smell which attracts dogs. 

 

Planktonic cyanobacteria: toxic algae blooms found in lakes appears as pea soup

Toxic algae blooms found in lakes appears as pea soup

 

Toxic algae mat on riverbed


Toxic algae found in rivers appears as mats on rocks

What to do if your pet dog has eaten toxic algae 

Please take care if walking your dog near any waterways to keep them away from anything that resembles toxic algae. 

If you think your dog has eaten toxic algae, treat it like an emergency and contact your vet immediately. Signs may include lethargy, muscle tremors, fast breathing, twitching, paralysis or convulsions. 

Report possible sightings of toxic algae

To report suspected toxic algae blooms, take a photo and call ORC’s Pollution Hotline on 0800 474 082. 

Prevent freshwater pests spreading

Check, Clean, Dry 

If you’re moving your gear between waterways, you must always clean all gear that has come into contact with water – use the ‘Check, Clean, Dry’ method below to help stop freshwater pests spreading.

Check 

Remove any algae or plant matter from your gear and leave it at the site (the river or lake bank) or put it in the rubbish. Don’t wash plant material down any drain. 

Clean 

There’s more than one option for cleaning your gear – choose the best one for your situation and your gear. 

Dry 

Ensure your gear is completely dry to touch, inside and out, then leave it to dry for at least another 48 hours before you use it (didymo can survive for months on moist gear). 

 

Lagarosiphon (oxygen weed) growing underwater

 

 

Lagarosiphon (Photo: G. Tooney)

 

 

Didymo (rock snot) caught on rocks in a river

 

 

Dried didymo looks like tissue paper

 

How to Check, Clean, Dry on the go

Download and print (or save to your phone) our helpful Check, Clean, Dry pocket guide before you head out. 

 

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