A warning has been issued to residents by Greater Wellington Regional Council [GWRC], after the detection of toxic algae in Waipoua River at Colombo Rd.
Toxic algae grow on rocks in the riverbed and form leathery dark green, brown or black mats.
Rivers are actively monitored across the region over summer for signs of the algae, which – if ingested – is deadly to dogs, and can make people very ill.
GWRC knowledge manager Dr Evan Harrison said a medium risk [amber alert] algae level has been detected in the Waipoua River, as well as the Pākuratahi River at Kaitoke Campground and the Hutt River.
“Very little toxic algae was detected in other Wairarapa rivers,” Harrison said.
“At amber or the medium risk level, there is 20-50 percent algal coverage in that area and no detached mats.
“The mats beneath the surface are a low risk to people and animals.”
At the amber alert level, Harrison said those in the area are encouraged to be cautious of toxic algae but to still enjoy the river.
“Where toxic algae is detected in one part of a river, it can be completely clear in other areas.”
Harrison said it is expected toxic algae levels will increase to red alert levels as the weather gets warmer and drier over the summer.
To trigger a red alert, algae coverage must exceed 50 per cent and/or detached algae mats are present.
High algal coverage means more oxygen is produced by the algae, causing mats to lift from the rocks and accumulate at river edges.
When this happens, it is vital that dog owners stay vigilant, Harrison said.
“Detached mats pose the biggest threat to dogs, who find their musty smell very appetising.
“Dogs can die from eating a very small amount of toxic algae – the size of a 50-cent piece can be fatal.”
Harrison advised to take your dog to the nearest vet immediately if you suspect it has eaten toxic algae.
And it’s not only dogs who need to be careful.
If ingested, Harrison said toxic algae can make humans very sick, with symptoms such as nausea, vomiting, and diarrhoea.
“Contact can also cause irritation of the skin, eyes, nose, and mouth,” Harrison said.
“Keep an eye on children, as they are more likely to put foreign objects or fingers that have touched algae in their mouths.
“In recent years, we have been fortunate that no people or animals have become sick from toxic algae in Wairarapa.”
It is recommended to seek urgent medical attention if experiencing a reaction after swimming or playing in a river, and to tell a doctor about toxic algae so they can inform Regional Public Health of the incident.
To know where it’s safe to swim, check the LAWA website for alerts and warnings before visiting your local river.
Masterton District Council monitors Henley Lake for signs of algae, and a council spokesperson has confirmed that the lake remains algae-free.
For more information on learning how to spot signs of toxic algae, visit Greater Wellington’s website.
