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Be responsible with Didymo algae

5 May 2005

Be responsible with Didymo algae this hunting season.

With duck shooting season starting this weekend, Biosecurity New Zealand is appealing to users of the Mararoa and lower Waiau rivers in Southland to guard against the spread of the invasive algae Didymosphenia geminata.

Didymo is an unwanted organism under the Biosecurity Act 1993. Under the Act, those knowingly spreading it can be liable for up to five years imprisonment or up to a $100,000 fine.

Biosecurity New Zealand Senior Adviser Dr Christina Vieglais says that at present there is no proven way to control Didymo in such a large river system, so measures are aimed at preventing its spread while more research is conducted. Although Didymo has been found in only the Mararoa and lower Waiau, it could easily spread to other rivers.

Didymo does not pose a significant human health hazard, but can affect water quality and cause itchy skin and eyes in swimmers. It forms large brown mats, which can smother the stream bed, potentially affecting any organism that needs the streambed to eat, breed, or seek shelter. It easily fouls fishing and boating gear, and can make stream beds extremely slippery.

“These two rivers are culturally significant, economically important and very popular for recreation. We don’t want to completely limit access, but we do need to intercept and educate those who are at risk of spreading Didymo. Even one cell in a drop of water could transfer it to other waterways. We’re relying on the public to be responsible, and so far they’ve been great, but we need that to continue,” says Dr Vieglais.

Biosecurity New Zealand has been working together with Fish and Game, DOC and Environment Southland to contain Didymo, and a public awareness campaign has been in place since Didymo was first noticed late last year. Warning signs have been placed on all public access points on the affected rivers, as well as on nearby unaffected rivers.

“The best way to avoid spreading it is not to use the rivers at all - or use only the Mararoa and lower Waiau rivers and nowhere else. Any equipment used in the water of these two rivers must be cleaned or dried thoroughly after use. Humans are the biggest risk of spreading it, but even a dog swimming in the river could spread the algae if its owner went to another river.”

Dr Vieglais says the good news is that cleaning Didymo from gear is very easy. It can be done by soaking and scrubbing an item for at least one minute in hot (60°C) water, a mild solution (2%) of household bleach, or a mild solution (5%) of nappy wash, salt, antiseptic hand cleaner or dishwashing liquid. Completely drying the item for 48 hours will also kill the algae.


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