Keeping your dog safe around water

Summer is the perfect time to take your dog to one of Canterbury’s precious freshwater sites – but, after some recent hot weather, it is timely to remind dog owners about the risks that cyanobacteria in rivers and lakes presents you and your dog.

Cyanobacteria (also called blue-green algae or toxic algae) makes animals extremely sick and can be fatal. Dogs are particularly at risk if they swallow the algae or algal mats when swimming or drinking from rivers, ponds and lakes.

Unfortunately, dogs are drawn to the musty smell of cyanobacteria and will investigate it – usually by eating or licking it. It is vital you know what to look for when visiting Canterbury’s freshwater sites.

Spotting cyanobacteria

cyanobacteria on a rock

Cyanobacteria appears on rocks as thick dark brown or black mats

In rivers: cyanobacteria (called benthic cyanobacteria) grows on the bottom of riverbeds and at the river's edge. It appears as thick dark brown or black mats that have a slimy or velvety texture and musty smell.

Our water quality and ecology team leader Shirley Hayward said if dog owners know what to look for in rivers, it's potentially life-saving for their canine friends.

"Look out for black mats on the river bottom or black/dark brown scums on the river’s edge. Dogs are really attracted to the musty odours in the scums and mats," Hayward said.

In lakes, ponds and lagoons: cyanobacteria (called planktonic cyanobacteria) is suspended in the water. Water can look cloudy, discoloured, or like it has small globules in it.

Planktonic cyanobacteria may not have obvious visual traits.

If you are in any doubt about the water quality, then keep your dog on a leash and away from the water.

When cyanobacteria is likely to appear

Cyanobacteria appears on rocks

Cyanobacteria appears on rocks as dark brown scums

The risk of cyanobacterial blooms increase during warm sunny weather, and with stable river flows.

We monitor more than 100 of the region’s most popular recreational water sites each week.

You can find the latest results and information about water quality and cyanobacteria risks on the Land and Water Aotearoa (LAWA) website, under the ‘Can I Swim Here?’ function.

However, we can’t monitor everywhere and river and lake users need to know what to look out for when planning to swim or let dogs in waterways.

Cyanobacteria poisoning symptoms

Symptoms in animals

Symptoms of cyanobacteria toxin poisoning in animals include:

  • lethargy
  • muscle tremors
  • fast breathing
  • twitching
  • paralysis
  • and convulsions. 

In extreme cases, death can occur 30 minutes after symptoms first appear.

If you are concerned, contact a veterinarian immediately. You or your vet can report to us any animal illness resulting from contact with cyanobacteria.

Symptoms in people

Cyanobacteria can also be harmful to people. If you have been in contact with water containing cyanobacteria, you may experience:

  • tingling or numbness around the fingertips and/or mouth,
  • breathing difficulty
  • gastrointestinal symptoms
  • or skin rashes.

If you feel any of these symptoms after contact with a waterway, seek medical advice from your doctor or contact Healthline on 0800 611 116 .

Resources on identifying cyanobacteria

We have resources available on how to identify cyanobacteria including this video, this printable PDF (745.85KB), and on our Health warnings page.