Wellington Scoop

Keep out of the water: poisonous algae in three rivers

Swimmers and dogs are being warned to keep out of the water in three regional rivers because of poisonous algae.

Toxic algal blooms have been found in the Hutt River between Birchville and Manor Park, and the Pakuratahi River at the Kaitoke campground, both in the Hutt Valley, and in the Waipoua River in the Wairarapa.

The Greater Wellington Regional Council says the recurring issue – it happens every year – is a result of water temperatures getting warmer and river levels dropping during summer.

The council’s senior environmental scientist, Dr Mark Heath, said the algae is toxic to humans and dogs.

“Toxic algae has increased to dangerous red alert levels in the Waipoua River over the last week, with detached mats washing up at the river’s edge so we strongly advise against swimming and letting your dog off the leash. It is very likely as the weather gets warmer that this risk will increase.”

“It’s important we all scrub up on the facts so we can all keep safe this summer, as toxic algae can be harmful to people and dogs. Algal mats grow on the rocks in the riverbed and form leathery dark green or black mats, which van break off and accumulate at river edges. As the algal mats dry out they can become light brown colour, and have a distinctive deep earthy or musty smell.”

Dogs are mostly at risk because they like the smell and taste of toxic algae. Even a small amount – about the size of a 50 cent piece, can be enough to kill a dog. Owners especially need to be vigilant of their dogs sniffing out toxic algal mats which can wash up at river edges.

If a person has been in contact with toxic algae and is feeling unwell, they should see their doctor or ring Healthline on 0800 611 116. Anyone with breathing difficulties or convulsions should seek urgent medical attention. If a dog is believed to have swallowed toxic algae, take it to the nearest vet immediately.

The council has also warned that bacteria from leaking pipes or run-off can contaminate swimming areas after heavy rain. “In general, a good rule of thumb is to stay out of fresh or sea water for 48 hours after rain, and always check for warning signs,” said Dr Heath.

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