Each summer from November to March, Environment Canterbury monitors more than 100 key recreational swimming sites weekly to check for cyanobacteria (toxic algae) that can be harmful to people, dogs, and stock.
Cyanobacteria is a naturally occurring blue-green algae with the potential to bloom, producing toxins that can harm or even kill people, pets and stock.
Blooms form when cyanobacteria multiply quickly, usually due to changes in environmental conditions such as warmer temperatures, sunlight, high levels of nutrients, or a change in river flows.
If the results show the water is unsuitable for recreation, Community and Public Health will issue health alerts. The health warning will be loaded to our website and signs will be erected.
However, signs may not be at all access points, so it’s important to know what to look out for. Also avoid swimming for 48 hours after there has been rainfall, as bacteria from roads, paddocks and other sources can wash into the waterway.
You can find the latest information about water quality and cyanobacteria risks for any monitored site in the country at the Land and Water Aotearoa (LAWA) website.
Keeping your dog (and yourself) safe
Unfortunately, dogs love the musty smell of cyanobacteria and are naturally drawn to investigating it – usually by drinking or licking the material. Livestock and humans are also at risk when it comes to potentially toxic cyanobacteria.
River cyanobacteria appears as dark brown/black mats attached to rocks along the riverbed and often has a strong earthy or musty smell. High river levels and flows will remove the algae bloom. However, detached mats can accumulate along the river edge and increase the risk of exposure to toxins.
If the water is cloudy or discoloured in lakes, ponds and lagoons (especially blue-green colouration, or has scums or small globules suspended in it), avoid all contact.
Not all cyanobacteria blooms are visible to the naked eye and toxins can persist after the blooms disappear. If you are in any doubt about the water quality, keep your dog on a leash and away from the water – if in doubt, keep them out.
Cyanobacteria poisoning: symptoms
Cyanobacteria can 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.
You may also experience 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.
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.