Kāpiti & Wairarapa river alert: Toxic algae in Waingawa and Otaki rivers at extreme levels

  • Published Date 14 Feb 2019

Toxic algae in the Waingawa and Otaki rivers are at extreme levels of more than 50% riverbed cover. Detached mats of dried algae are widespread along the river margins. Mats have also been found in the Waikanae River at Jim Cooke Park.

The algae is shiny brown/dark green and coats submerged riverstones. When it dies it floats to the surface and forms brown mats at the water's edge. It is important to keep an eye on babies and toddlers who are inclined to put objects in their mouths. Seek emergency medical attention if anyone in your group swallows toxic algae.

Contact with toxic algae can cause symptoms such as skin irritation, nausea, vomiting, numbness, tingling or muscle twitches. You may feel short of breath.  If you develop these symptoms following contact with the river, please contact your doctor or Healthline on 0800 611 116.  Swallowing toxic algae has the potential to cause serious health issues such as convulsions or loss of consciousness, symptoms which need urgent medical attention.

This is the first time guideline levels have been exceeded in Otaki River. The affected area extends from Hautere all the way down to the river mouth. The stretch of the river below SH1 is particularly bad. Swimmers should avoid this reach as the risk is very high.

Swimmers should also avoid the Waingawa River.

Caution is also advised when choosing a swimming spot in the Waikanae River downstream of SH1, due to the presence of detached mats.


Keep dogs on leashes in these areas. Dogs are at greatest risk from toxic algae because they love the smell of it and will eat it if they can. During a bloom, they must be kept on a leash along the river bank. If you suspect your dog has eaten toxic algae (even if only a coin-sized amount) take it straight to the vet.

We strongly advise that dogs be kept on leashes by the Pakuratahi River from SH2 to its confluence with the Hutt River in Kaitoke Regional Park. We also strongly advise people not to swim in this area.

The Waipapa Stream (near rocks) and the Hape Stream also on the Red Rocks walking track (near the start of the track) both have significant blooms. The streams are not swimmable but dog walkers should be careful.

Know your enemy

Greater Wellington monitors popular swimming spots weekly throughout the summer. We will issue an alert if toxic algae reaches unsafe levels, but please learn to recognise and avoid it.

When the weather is dry our rivers can produce toxic algal blooms, especially where the water is already shallow. We monitor the toxic algae in rivers in the region, and work with councils across the region to keep river and stream users informed.

Given the rapid growth of toxic algae, and its potential change in coverage between weekly monitoring points, people are also urged to get educated. See pictures below and also check out information signs around popular swimming holes, and visit Greater Wellington's Is it Safe to Swim? website and Facebook page for more information.

Updated April 28, 2022 at 10:35 AM

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