Why is Didymo a pest plant?
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.
To slow the spread of the invasive alga didymo and other aquatic pests in New Zealand waterways, MAF Biosecurity New Zealand requires all used freshwater fishing equipment brought into New Zealand to be clean and dry.
From mid-October 2007 MAFBNZ's Import Health Standard for Equipment associated with Animals or Water will be updated to require MAFBNZ staff to treat all used freshwater fishing equipment they determine or suspect is NOT COMPLETELY DRY (inside and out), regardless of whether it has been cleaned before coming to New Zealand.
Felt-soled waders and boots are of particular concern. Recent research has revealed these items pose a particularly high-risk of spreading didymo as they are likely to come into direct physical contact with didymo cells (e.g., stepping on or brushing against algal mats) and the thick, absorbent and slow-drying nature of the material encourages cell survival, increasing the risk of spread between waterways. So felt-soled footwear has been banned in all of New Zealand waterways as of 1 October.
Good freshwater hygiene is important for everyone. Travelling anglers have an important role to play in protecting the environments they visit.
If you are moving between waterways, you must 'Check, Clean, Dry' all equipment you have used. Research has shown this is the best way to slow the spread of didymo and other aquatic pests. Detailed cleaning instructions for specific items such as felt-soled waders have been developed.
New Zealand rivers offer some of the best fishing in the world. Help us to keep it that way.
News Release: Didymo has just been discovered in the wild and beautiful Karamea River in the Kahurangi National Park. That means the wonderful tributaries like the Crow and the Ugly will soon be affected. If you are changing waterways YOU MUST CLEAN YOUR WADING GEAR!
Didymo was also recently found in the Waitahu River, a tributary of the famous Inangahua River. The Waitahu is well known for its trophy trout and easy access.
In Otago, didymo is found in Lake Dunstan, and the Clutha, Hawea, Von, Fraser, Makarora, Wilkin, Motatapu and Matukituki rivers, and possibly their tributaries.
In Southland, didymo is found in the Oreti, Aparima, Mararoa rivers. There was some suggestion that didymo had been found in the Greenstone River but this has not been substantiated.
Further north, didymo has been found in the Buller, Wairau, Cobb rivers and some of their tributaries.
A full list can be found here http://www.biosecurity.govt.nz/files/pests-diseases/plants/didymo/didymo-affected-waterways.jpg
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.
As the 'tails' of the algae get longer they become white in colour
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 NZ rivers, please contact:
- Ministry of Agriculture and Fisheries on 0800 809 966.
If you don't want to fish in such waters -
Remember to check, clean and dry all equipment, before you leave any lake, stream or river.
If you are moving between waterways, you must Check, Clean, Dry:
CHECK: Before you leave a river or lake, check items and leave debris at site. If you find any later, treat and put in rubbish. Do not wash down drains.
CLEAN: There are several ways to kill didymo. Choose the most practical treatment for your situation which will not adversely affect your gear.
Non-absorbent items
Detergent: soak or spray all surfaces for at least one minute in 5% dishwashing detergent or nappy cleaner (two large cups or 500mls with water added to make 10 litres); OR
Bleach: soak or spray all surfaces for at least one minute in 2% household bleach (one small cup or 200mls with water added to make 10 litres); OR
Hot water: soak for at least one minute in very hot water kept above 60 °C (hotter than most tap water) or for at least 20 minutes in hot water kept above 45 °C (uncomfortable to touch).
Absorbent items require longer soaking times to allow thorough saturation.
For example, felt-soled waders require:
Hot water: soak for at least 40 minutes in hot water kept above 45 °C; OR
Hot water plus detergent: soak for 30 minutes in hot water kept above 45 °C containing 5% dishwashing detergent or nappy cleaner; OR
Freezing any item until solid will also kill didymo.
DRY: Drying will kill didymo, but slightly moist didymo can survive for months. To ensure didymo cells are dead by drying, the item must be completely dry to the touch, inside and out, then left dry for at least another 48 hours before use.
If cleaning or drying is not practical, restrict equipment to a single waterway.
NOTE: The thicker and denser the material, the better it will be at holding moisture (and live cells), the slower it will be to dry out and the more difficult it will be to soak completely with cleaning solutions.
When cleaning equipment, we recommend that you:
soak porous materials for longer than the specified decontamination times to ensure cleaning solution has soaked right through the item before soaking for the required decontamination time
choose a decontamination solution that will not adversely affect your equipment
follow manufacturer’s safety instructions when using products
dispose of cleaning waste well away from waterways
