While it may look unpleasant and sometimes smell, most algae in our waterways is harmless. However, some species found in Auckland can be harmful to people and animals if ingested.
“The only way to work out if algae are harmful is through laboratory testing. Auckland Council runs regular water quality sampling throughout the summer, and will place warning signs at places where it is best to avoid contact with the water,” said Craig Mcilroy, General Manager Healthy Waters.
Algae occur naturally in Auckland’s lakes, streams and waterways, flourishing as the weather warms up for summer. They can also bloom following an increase in nutrients such as fertiliser run off or sewage effluent, particularly after heavy rainfall.
Algal blooms can cause freshwater and seawater to turn green, red, bright blue, white, cloudy or foamy, and are most likely to occur in calm, sheltered water.
Best avoided
Freshwater algal blooms caused by toxin-forming cyanobacteria are best avoided. Also called blue-green algae, it can turn the water mustard, muddy-green, blue-green and even a vibrant sky blue colour.
In seawater, algae often turns the water red or brown in what is known as a red tide.
The wind may carry algae into coastal shallows or lake shores, where they accumulate as surface scums. These should be avoided as blooms are more likely to release their toxins when in highly concentrated scums.
“We would urge caution before swimming in water affected by surface scums or algal blooms. In addition to it potentially being harmful if ingested, the blooms discolour the water and obscure underwater hazards, posing a risk of drowning,” says Craig.
Keep dogs safe around Cyanobacteria
In summer and autumn, toxic cyanobacteria can form mats covering boulders in rocky streams. With a moss-like appearance, its colour is usually a greenish dark brown. It contains a very powerful nerve toxin and is especially harmful to dogs.
Thankfully it’s not common in Auckland, as it most often grows in open, rocky rural streams.
If you're travelling outside the region make sure you look out for it, especially if you're visiting places with a history of cyanobacteria. If you walk your dog near a rocky stream, be especially vigilant as dogs are drawn to it, and will readily eat the dried mats.
If you are concerned your dog has eaten cyanobacteria, you should contact a veterinarian immediately. If you have come in physical contact with the mats, you must wash your hands thoroughly before consuming food.
Information about water quality and safety at 84 beaches across Auckland can be found at safeswim.org.nz. If you are concerned about an algal bloom, please call us on 09 301 0101.
