Wellington Scoop

Three rivers now dangerous for swimmers and lethal for dogs

Three Wellington region rivers are now dangerous for swimmers and dogs because of poisonous algae. The Regional Council today issued a warning about two rivers in the Kāpiti Coast area, a week after it issued a similar warning about the Hutt River.

News from Greater Wellington Regional Council
Swimmers are advised to take caution while dog owners should keep dogs on leashes or avoid two river sites along the Kapiti Coast with toxic algae, including detached algal mats.

The sites are located at the Otaki River at State Highway One and the Waikanae River at Jim Cooke Park

Waikanae River at Jim Cooke Park

The council’s Marine and Freshwater Team Leader Dr Evan Harrison said “Toxic algae has increased to amber levels at the site, meaning we strongly advise caution to swimmers and to check the LAWA website regularly for updates before getting in the water”.

The warning bears greater significance for dog owners as dogs like the smell and taste of the algae and a small piece, only around the size of a 50c coin, is enough to kill a dog.

“The risk is higher with detached algal mats being found at both sites, meaning the algae has broken off rocks in the riverbed and accumulated at the rivers edge, within easy reach for dogs,” said Dr Harrison. “With this warm weather, caution is advised for people and their pets until this warning has been removed from the LAWA website.

“We’ve seen sites that were safe to swim in move to dangerous warning levels within a matter of days. The warm weather is accelerating that and it’s important to check the latest status on LAWA.” .

The council is monitoring popular swimming spots around the region on a weekly basis to ensure the community knows when where it’s safe to swim.

Members of the public who think they or their dogs have been in contact with toxic algae should see your doctor or ring Healthline on 0800 611 116 and for their dogs, take it immediately to the nearest vet.


News from Greater Wellington Regional Council – 15 January
Swimmers and dog owners are advised to avoid areas of the Hutt River from the Moonshine Bridge down to just upstream of Taita Rock (but not including Taita Rock), as high levels of toxic algae including detached algal mats have been identified at two monitoring sites along the river.

Greater Wellington Marine and Freshwater Team Leader Dr Evan Harrison said: “Monitoring data at the Hutt River at Silverstream Bridge, and Hutt River upstream of Silverstream bridge returned red alert levels of toxic algae. This means there are high levels of cyanobacteria present rendering the site unsuitable for swimming and it should be avoided”.

Toxic algae presents a significant health risk as swallowing water containing the bacteria can make people very sick, with pieces as small as a 50c coin enough to kill dogs.

The presence of detached algal mats carries increased risk as the algae has broken off rocks and can wash up on the river’s edge where dogs, who love the smell and taste, can easily spot it. Young children should also be watched closely if in the area to ensure they do not come into contact with toxic algae.

The regional council monitors a large proportion of freshwater and coastal sites around the region, publishing updated safe swimming data weekly on the LAWA website.

“There are plenty of spots we monitor, and a suitable swimming location may be just a stone’s throw away. Excluding Silverstream, there are four further locations we monitor in Upper Hutt.

“As Summer rolls on, people taking the plunge with or without their four-legged friends should continue to check online before hoping into the water and be aware of what toxic algae looks like.”

Members of the public who think they or their dogs have been in contact with toxic algae should see a doctor or ring Healthline on 0800 611 116 and for their dogs, take them immediately to the nearest vet.

Earlier: Poisonous algae in Ruamahanga River

Additional information on Toxic Algae:

What causes it:

Toxic algae in our rivers are cyanobacteria, which is commonly referred to as blue-green algae. Cyanobacteria are naturally present in all New Zealand waterways, but can grow to dangerous levels when the weather is particularly hot and dry.
During summer, we tend to see more of these harmful blooms in our region’s rivers, making the swimming sites especially dangerous for people and dogs.
These blooms last until there is a flushing event due to heavy rain. The LAWA website will be updated when it is safe to enter the water.

Staying safe:


Toxic algae is a health risk to people, particularly young children. Because kids are inquisitive and more likely to pick up toxic algae and then put their fingers in their mouths, special care should be taken when swimming with them.
Swallowing water containing 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.


Toxic algae is lethal to dogs. It contains a ‘neuro-toxin’ which kills dogs by blocking their nerves from communicating with each other.
If there has been an alert issued, or you think you have spotted a toxic algal bloom, keep your dog on a lead and away from the water to ensure they don’t eat any algal mats.
In extreme cases, a dog may die within 30 minutes of eating toxic algae, so we encourage people to remember that preventing poisoning is better than any known treatment.
Symptoms in dogs include seizures, severe vomiting and diarrhoea. If your dog has any of these symptoms, take it to the nearest vet immediately. Make sure to tell your vet that you think it may have ingested toxic algae.

How to spot it:

Toxic algae blooms appear differently in lakes and rivers.


Look for black, green or brown slime on rocks, or brown or black “mats” at the river’s edge that have a velvety texture and earthy/musty smell.
If you see toxic algae, be cautious and avoid that river site, particularly if you have a dog.
Check for alerts on the LAWA website, which provides live updates on where it is safe to swim.


Lakes in the Wellington region are not part of our monitoring program, as river swimming spots are much more popular. However, we encourage you to know what to look for in lakes as well as rivers.

If the water has a “pea soup appearance”, it could contain toxic algae. Discoloured, cloudy water with small green blobs suspended in it should be avoided.

What the regional council is doing about it:

Due to the impact of hot dry weather on toxic algae blooms, there is no quick or obvious solution to prevent them. For this reason, people are strongly advised to learn what toxic algae looks like, and swim elsewhere if they see it.
The council works with other councils and Regional Public Health to monitor the safety of our waterways, and issue warnings when blooms occur.

This includes signs at key sites where toxic algae is considered a hazard, and updates online.

Content Sourced from scoop.co.nz
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