Toxic algae health risk for river users

River monitoring by Greater Wellington Regional Council (GWRC) has shown increased coverage of toxic algae. Photo / AP

People are being warned to protect themselves and their dogs against toxic algae in Masterton's Waipoua River after levels increased.

Weekly river monitoring by Greater Wellington Regional Council (GWRC) has shown increased coverage of toxic algae at its Colombo Rd monitoring site presenting a potential risk to river users.

Toxic algae, or cyanobacteria, form brown or black clumps on river beds and can kill livestock and dogs. The clumps can peel off and often wash up on the river's edge where dogs can easily come into contact with them.

Along with Masterton District Council and Regional Public Health, the regional council is urging river users to be careful, and warning signs have been put up.

GWRC environmental monitoring officer Brett Cockeram said the algae has a pungent smell and often clumps together once it is washed off the rocks.

Mr Cockeram said the spot next to the Colombo Rd Bridge was quite popular with people and dogs, and the last death of a dog he could recall happened in 2010.

The algae has been an ongoing problem but "wasn't quite so bad last year" because of the rain. GWRC aquatic ecosystems and quality team leader Juliet Milne said toxic algae can be abundant in many New Zealand waterways during summer.

"The warm weather in the Wairarapa and the lack of heavy rain in the Waipoua catchment are key factors behind the increase," Ms Milne said.

"The risk to river users and dogs is likely to remain until there's significant rainfall to flush the algae away."

Contact with toxic algae can cause vomiting, diarrhoea, skin irritations and other symptoms in humans.

Tips for keeping safe

• Avoid touching and swimming near the algae, especially where there are warning signs.
• Make sure dogs are on leads.
• Take dogs to a vet immediately if you think they have come in contact with algae as it can be toxic.
• If you have visited a river and think you are having a reaction to toxic algae contact your GP immediately.

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