Read about Didymosphenia Geminata or "Didymo" for short - a freshwater exotic algae contaminating South Island, New Zealand, rivers...

Didymosphenia Germinata, or "Didymo" for short - also known as rocksnot - a freshwater exotic algae contaminating South Island, New Zealand, rivers...

Didymo is a member of a group of single celled aquatic plants(freshwater algae)known as diatoms. Didymo is an exotic( non-native)organism to New Zealand, and has legally been declared an unwanted organism under the Biosecurity Act 1993.

Didymo was first detected in the lower Waiau and Mararoa Rivers in Southland in October 2004.Since then Didymo has been found in the Tasman District, the Otago region and additional rivers in Southland.In December 2006 Didymo was detected for the first time in Fiordland National Park.

It is likely that Didymo will have an impact on the numberof recreational and commercial activities in New Zealand, and as well as cultural values and biodiversity. As the man said, it is a bit of a worry!


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Why is Didymo a pest plant? How do I identify it?

Didymo - also known as 'rock snot' - is a freshwater diatom (a type of algae.) It can form massive blooms on the bottom of streams, rivers and lakes, and its spread is highly undesirable.

This microscopic pest can be spread by a single drop of water. Even if you can't see it, you could be spreading it.

The alga is a native of northern Europe and North America, and was first reported in New Zealand in 2004. Biosecurity New Zealand has since declared the entire South Island an Outbreak Control Area for didymo. This means rivers and lakes remain open to angling, boating and other recreational activities, but all gear should be cleaned before going from one waterway to another.

In Otago, didymo is found in Lake Dunstan, and the Clutha, Hawea, Von, Fraser, Makarora, Wilkin, Motatapu and Matukituki rivers, and possibly their tributaries.



How do I identify Didymo?

The alga 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.







Pictures of Didymo, mats and tails above.


In Otago, Didymo has been found in Lake Dunstan, the Clutha, Hawea and Von rivers, and possibly their tributaries. It has also been identified in a number of other rivers in the South Island.

Suggested ways to avoid spreading didymo:

All river users are urged to take care not to spread the alga from one waterway to another.

Before you leave any river or lake:

Check - remove all visible threads or clumps of weed and algae from gear and clothing.

Clean - soak or scrub all items of equipment for at least one minute with either:

hot (60 degrees C) water, or
2% solution of household bleach, or
5% solution of salt or nappy cleaner, or
5% solution of dishwashing detergent, or
5% solution of antiseptic hand cleaner.
Dry - after cleaning equipment, or if cleaning is not practical (e.g. animals), dry until touch dry then leave for a further 48 hours before entering another waterway.

A number of cleaning stations have been set up in the Upper Clutha area for the summer, to help stop the spread of didymo. The unmanned stations will be identified with signage. People can pull in there to wash and disinfect boats and fishing gear that may have come into contact with infected waters.

If you come across any suspicious looking algae in Otago rivers, please contact:

Otago Regional Council on 0800 800 033, or
Ministry of Agriculture and Fisheries on 0800 809 966.
Remember to check, clean and dry all equipment, before you leave any lake, stream or river.

It has not yet contaminated North Island rivers.
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