Long, hot summer bad for toxic algae problems

Hot, dry weather that has bathed Wairarapa in sunshine for several weeks and looks likely to continue well into March has worsened toxic algae problems in the Ruamahanga River, especially at the popular picnicking spot at Kokotau Bridge.

As a result, organisations monitoring the river have joined forces to urge people using the river at Kokotau - particularly dog owners - to avoid doing so.

Warning signs have been put up to that effect.

Summer Greenfield, senior environmental scientist with Greater Wellington Regional Council, said the council monitored toxic algae from Doubles Bridges on the Opaki-Kaiparoro Road to Martinborough and at specific sites in the Waipoua, Waingawa and Waiohine Rivers.

Algae might also be growing in rivers not monitored by the council.

Mrs Greenfield said Kokotau was the only site of 13 monitored sites that had so far been classified as a high-risk area.

"People need to be aware of what toxic algae looks like so they can avoid it wherever it may be," she said.

Toxic algae - or cyanobacteria - form brown or black clumps on riverbeds and can kill dogs or livestock.

The clumps can peel off and often wash up on the river edge, where dogs can easily eat bits of the clump.

Eating the algae can kill dogs very quickly.

In humans, coming into contact with toxic algae can cause vomiting, diarrhoea, skin irritations and other allergy-type symptoms.

Mrs Greenfield said the recent hot weather in Wairarapa was the key factor behind the proliferation of toxic algae and that would remain until there had been enough rain to flush the rivers.

Dog owners walking or exercising dogs near waterways and who thought they could see toxic algae should put the dog on a lead and move away from the river's edge, Mrs Greenfield said.

If they suspected the dog had eaten algae it was essential to get the animal to a veterinarian immediately.