8 February 2019

Waingawa River toxic algae alert: Effect of heat wave ripples through region's rivers

Toxic algal concentrations in the Waingawa River now exceed guideline levels. This is the first time this summer that the Waingawa River has exceeded guidelines. Dog owners who access the Waingawa River from South Road and/or Hughes Line are advised to keep their dogs on leashes. Please don't swim in the general vicinity.

Toxic algal levels have also increased in the Otaki River, but are currently not at warning levels. However Toxic algal levels have decreased in the Hutt, Waipoua and Waikanae rivers, but remain steady in the Pakuratahi River (Kaitoke Regional Park).

The current warning for the Hutt River upstream of the Silverstream bridge warning, which extends from Moonshine Bridge to Fairway Drive Bridge, remains in place even though toxic algal levels have slightly decreased and are now below the guideline level of 20% of riverbed cover. Similarly, the current warning for the Pakuratahi River site remains in place.

We strongly advise that dogs be kept on leashes by the Hutt River between Moonshine Bridge and Fairway Drive Bridge, or in 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 these areas where warnings are currently in place.

The algae is shiny brown/dark green and coats submerged riverstones. When it dies it floats to the surface and forms small 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 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.

Dogs

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.
Greater Wellington
Greater Wellington is monitoring 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.

Heatwave stats

Water temperature last week during the peak of the heatwave hit a whopping 27°C at our Taita Gorge monitoring site, on Wednesday (Waitangi Day) the peak water temperature was 21.1°C. This may help explain the decrease in toxic algae in the Hutt River.

Know your enemy

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.

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