Toxic Algae in the lower Waipoua River
16 October 2018
There is a toxic algal bloom in the lower Waipoua River, and Greater Wellington Regional Council is advising caution when swimming or dog walking along the riverbank.
The bloom was discovered at a monitoring site at the Colombo Road bridge on Wednesday 10 October.
“The bloom is at fifteen to twenty percent coverage of the riverbed which is approaching our guideline alert levels”, said Senior Environmental Scientist Mark Heath.
“Small mats of it are lifting and floating along the bank. These mats are a concern because toxic algae can be deadly if swallowed. Dogs love the smell of them and will eat them if they get the chance. They need to be kept on a leash if you’re down by the river.”
Toxic algae is potentially deadly to humans although there has never been a recorded case in New Zealand. But as toxic algal blooms have increased in frequency and size in recent years, Mark Heath is concerned that babies and toddlers could be at risk if levels rise.
“When a river reaches red alert level, there’s a lot of toxic algae washing up and we’re starting to worry about small children picking it up and eating or mouthing it. It’s very dangerous. There’s also potential for kids horsing around in the river to accidentally swallow it.”
Above Masterton the Waipoua River runs through rural private land where Greater Wellington does not have monitoring sites. While the upper Waipoua is not as prone to toxic algal blooms as the urban stretch, people using the river there are advised to check the river and banks before swimming or dog walking, and avoid contact with the algae.
Toxic algal blooms are caused by a combination of warm weather, high nitrogen concentrations and persistent low water flows. They are usually cleared (or “flushed”) by a period of high rainfall.
Greater Wellington will be monitoring all the region’s rivers throughout the summer. Toxic algae warning signs will be placed at river entrances and there will be an awareness campaign helping people to identify it. If or when rivers reach red alert levels, Greater Wellington will inform the public through social and traditional media.
If a person swallows even a small amount of toxic algae (coin sized) this is a medical emergency – call an ambulance or go straight to hospital. If you have health issues after contact with toxic algae (e.g. skin contact) ring your doctor or Healthline 0800 611 116.
If your dog swallows even a small amount of toxic algae (coin sized) seek urgent veterinary attention.