Look out for toxic algae in our rivers and lakes this summer
Environment Canterbury media release: 27th November 2024
If you are heading to a river or lake to cool off this summer, check for toxic algae (cyanobacteria) in and around the water, it can cause serious harm to people and animals.
Toxic algae occur naturally in waterways, but when the amount increases, it blooms. These blooms can produce toxins that cause illness if ingested.
There are many factors that drive the growth of the algae including water temperature, flow rate as well as nutrients present.
Manager for water and land science Dr Elaine Moriarty says that if dog owners know what to look for in rivers and lakes, it can be lifesaving for their canine friends.
"Unfortunately, dogs are drawn to the musty smell of toxic algae and will investigate it – usually by eating or licking it.
"It only takes a teaspoon to cause fatal consequences if ingested by dogs," Moriarty says.
Toxic algae is a natural algae found in rivers and lakes in New Zealand. In the summertime the algae can increase in size and bloom.
How to spot toxic algae
We monitor water quality at recreation sites over summer for toxic algae . The assessments are based on the amount of toxic algae needed to pose a risk to human health. It is not always possible to observe small amounts of toxic algae that could still be dangerous for dogs.
"Small amounts of toxic algae can be present in a waterway that is listed as suitable for swimming or it can be present in areas that we don’t monitor.
"The best way people can protect their dogs, is by knowing what toxic algae looks like and avoiding it.
"If you’re ever in doubt about the water quality, then keep your dog on a leash and away from the water’s edge." Moriarty said.
What to look for in rivers
Toxic algae grows on the bottom of river beds. It appears as thick dark brown or black mats that have a slimy or velvety texture and musty smell.
These mats can come loose and wash up on the edge of the rivers, or form ‘floating rafts’ in shallow areas. As they dry out, they turn light brown or white and look like dried leaves or cowpats producing a strong musty smell.
What to look for in lakes, ponds and lagoons
Toxic algae is most often suspended in the water of lakes, lagoons and ponds.
When it blooms, it can make water look cloudy, discoloured, or like it has small globules in it.
Toxic algae poisoning symptoms
Symptoms of cyanobacteria toxin poisoning in animals include lethargy, muscle tremors, fast breathing, twitching, paralysis, and convulsions. If you suspect your dog is suffering from cyanobacteria poisoning, contact your vet immediately.
For humans, 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.
Find out more about how to spot toxic algae (Environment Canterbury).
Watch a video on identifying toxic algae in rivers (YouTube).