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Public Support Needed To Limit Spread Of Didymo

10 December 2004

Public Support Needed To Limit Spread Of Didymo

Information officers will be patrolling the Lower Waiau and Mararoa rivers to ensure the public are taking the appropriate measures to limit the spread of the invasive algae Didymosphenia geminata a (Didymo) Biosecurity New Zealand senior adviser Amelia Pascoe said today.

Biosecurity New Zealand (BNZ) has been working with Environment Southland, NIWA, Department of Conservation (DOC), Fish & Game and other organisations to determine the extent of Didymosphenia geminata populations in Southland river systems.

A technical advisory group (TAG ) convened by Biosecurity New Zealand, which met in Te Anau recently, concluded that Didymo has probably been present in the two river systems for up to two years. Its discovery in October is probably related to the fact that Didymo was in bloom.

“We still know very little about Didymo so our strategy is focused on attempting containment and researching how far it has spread and the treatment options river users can use to kill the algae to ensure they don’t spread it to other waterways.

“It appears this algae has not been eradicated anywhere else in the world so control and containment are likely to be our only options. Biosecurity New Zealand and Environment Southland have launched a campaign to inform the public about the risk of spreading Didymo and the actions they can take to stop the algae being spread to other river systems.

“We have put up signage on Southland and Otago waterways to inform people they should avoid using the Lower Waiau and the Mararoa and providing them with information of how to clean any gear that does come into contact with these rivers. The information officers will be advising people on how to clean their gear and ensuring people are aware of the problems the algae can cause.

Under the Biosecurity Act 1993, anyone who knowingly spreads Didymo will be liable of a fine of up to $100,000 dollars and/or imprisonment of 5 years.

Overseas Didymo has degraded some fishing rivers and there is some anecdotal evidence that it impacts on the ecology of the rivers by limiting the range of food for some species and it also clogs up water intakes.

Key Facts

BNZ has declared Didymosphenia geminata to be an unwanted organism under the provisions of the Biosecurity Act 1993.

Didymosphenia geminata is found in cooler northern hemisphere river systems. It is not known how it came to be established in Southland.

This algae looks liked it would be slim but actually feels like wet cotton wool and is known in the United States and Canada as “rock snot.” It can form flowing rat tails and when dry it can turn white and look like tissue paper.

Until the extent of Didymosphenia geminata infestation in other river systems is known and management options are better understood, BNZ, DOC and Environment Southland with the help of Fish and Game are putting in place measures to limit the spread beyond the Waiau and Mararoa river systems.

The Ministry of Health considers Didymosphenia geminata to be a nuisance species and not a significant human health risk. Swimmers may experience scratchy, red, watery eyes after swimming. Water taste and odour maybe affected but overall water quality does not appear to be degraded by this algae.

If people do use the river they should ensure that any boats, fishing equipment and other possessions that come into contact with the river and the Didymosphenia geminata algae should be thoroughly cleaned before they are exposed to other river systems. A bleach solution or nappy cleaning products should be used to effectively kill the algae.


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