Didymosphenia geminata

Background

Didymosphenia geminata was found in the lower Waiau and Mararoa rivers in October 2004.

The natural distribution of this algae is northern Europe and northern North America. Its presence in New Zealand may be the first in the southern hemisphere. It is not considered a significant human health risk but is considered an invasive species overseas.

During September 2005 Didymo was also discovered in the upper Waiau River and the upper Oreti River. In addition, sites were also found in the upper Buller, Hawea and Von Rivers

Description

Didymosphenia geminata is a freshwater diatom (a type of algae). It can form massive blooms on the bottom of streams, rivers and lakes.

The algae attaches itself to the streambed by stalks and can form a thick brown layer that smothers rocks, submerged plants and other materials. It forms flowing 'rats tails' that can turn white at their ends and look similar to tissue paper.Although the algae appears slimy, it feels like wet cotton wool.

Stop the spread

Didymo is made up of cells that cannot be seen with the naked eye until large colonies form. It only takes one of these cells to survive and be transported to nearby waterways for this invasive algal species to spread. These cells thrive in freshwater and by cleaning with freshwater you are helping them to keep them alive.

To ensure you do not spread Didymo, wherever possible restrict equipment, boats, clothing and other items for exclusive use in a single waterway. If you are moving items between waterways you must:

Check: Before leaving the river, remove all obvious clumps of algae and look for hidden clumps. Leave them at the affected site. If you find any later, do not wash them down drains. Treat them with the approved cleaning methods below, dry them and put them in a rubbish bin.

Clean: Soak and scrub all items for at least one minute in either, hot (60°C) water, a two percent solution of household bleach or a five percent solution of salt, nappy cleaner, antiseptic hand cleaner or dishwashing detergent. A two percent solution is 200 mls a five percent solution is 500 mls (two large cups), with water added to make 10 litres.

Dry: If cleaning is not practical (i.e. livestock), after the item is completely dry to touch, wait an additional 48 hours before contact or use in any other waterway. (The reason for this substantial change is to reflect the new key message that has been developed by the BNZ).

Equipment that remains damp or could have pockets of trapped moisture after use will require longer drying times because the 48 hour drying time begins after dampness and trapped moisture have evaporated. Some equipment may never ready complete dryness depending upon how and where it is stored (shoes, waders, life vests, wetsuits, spay skirts, jet boat intaks, tyres etc) and therefore should always be chemically treated.

Under no circumstances should fish, plants or other items be moved from an affected waterway to an unaffected waterway.

View Didymo Cleaning Cards

Print these cards out and keep them handy, or post them up in key places. The cards are available in five languages:

English (472KB)  |  German (169KB)  |  Japanese (224KB)  |  Korean (168KB)  |  Simplified Chinese (255KB)

Controlled Area Notice

For Didymo controlled area notices, please see the following:

Clarification of South Island Didymo Controlled Area (89KB)

Stakeholder Update 30 August 2006

Read the Stakeholder update here. (50KB)