Didymo

Didymosphenia geminata

Didymo

Didymo

Legal Status: Unwanted Organism - MPI
Status in New Zealand: Investigating
Organism: Marine and freshwater plants

The standard decontamination treatments are included in the Check Clean Dry message above. Further information is available in a table comparing the effectiveness of methods and products tested on didymo survival, published in the Didymo Survival Study Report. This table includes information on using reduced concentrations of decontamination products for longer soaking times to suit high volume commercial users who wish to soak gear overnight at less expense to themselves, their business and the environment.

Unless otherwise stated, all dilutions are given as volume of cleaning product/volume of total water (v/v). For example, a 5% solution is made by mixing 50 ml of product with water added to make 1000 mls (1 litre) total.

Information for event organisers

The table below describes in more depth how to clean specific items. Unless stated otherwise (such as for felt-soled waders and boots), all of the decontamination options are effective on all items, provided that absorbent items are thoroughly soaked.

Felt-soled waders and boots Felt-soled waders are not permitted for angling for sports fish in New Zealand. The Anglers Notice issued under the Conservation Act 1987 states at 2.4 "No person shall fish for sports fish by using felt soled waders or footwear incorporating of having attached a sole of felted, matted or woven fibrous material when sports fishing."

Fishing footwear containing absorbent material, such as felt-soled waders and boots, poses a high risk of didymo transfer—these items are likely to come into direct physical contact with didymo cells (e.g., stepping on or brushing against algal mats), and the moisture retained in these goods helps cell survival.

Choose one of the following treatments specific to felt-soled waders and boots:

Hot water: If hot water alone is used, careful attention is needed to ensure the temperature of the water is maintained at no less that 45 °C for 40 minutes to ensure the interior of the felt reaches a sufficient temperature to kill all cells;

OR

Hot water and detergent: The entire felt sole and boot needs to be completely immersed for 30 minutes in hot tap water kept above 45 °C (uncomfortably hot to touch) containing 5% dishwashing detergent or nappy cleaner;

OR

Freeze until solid: The time required until the boot is frozen solid will vary depending upon the grade of material, how much moisture it contains and the efficiency of the freezer. Freezing overnight should work in most instances.

Drying: Relying on ambient drying as a stand-alone treatment for decontaminating highly absorbent risk goods such as felt-soled waders and boots is not recommended in situations where use between waterways is frequent (daily, weekly or even monthly). Drying should only be relied upon as a decontamination treatment if great care is taken to actively and completely dry the felt (such as by using a heat source where temperatures around the felt are assured of reaching 30 °C). Once the felt appears dry, complete dryness must be confirmed by a tactile inspection of the felt pile to the base of the fibres. Once completely dry, items must remain dry for at least 48 hours before use in another waterway.

These instructions for decontaminating felt soled waders and boots can be used for other absorbent materials.

If you do not want to decontaminate your gear, you should restrict use to a single waterway.
For the following items, use the treatment options given in the Check Clean Dry message and for more options see the Table of Didymo Survival Results above.
Fishing and eeling equipment All rods, reels, fishing lines, flies, tackle boxes, nets, clothing and other equipment should be thoroughly soaked in a decontamination solution. Alternatively, use the hot water treatment or freeze gear until solid. Allow longer time for absorbent items.

After treatment, items may then be rinsed with water that has come from a town water supply.

Drying is an acceptable alternative method, provided that all components (such as backing lines, nets and clothing) are completely dry to the touch, inside and out, and then left dry for at least another 48 hours before entering a different waterway.

If you do not want to decontaminate your gear, you should restrict use to a single waterway.
Whitebaiting equipment Nets and other items made of absorbent material can be decontaminated by soaking in a 5% solution of dishwashing liquid or nappy cleaner for as long as it takes to thoroughly saturate the item, plus for at least an additional minute to kill didymo cells trapped deep within the cracks, crevices and absorbent parts of the item. Non-absorbent items such as tyres, trailers and buckets can be soaked or sprayed with the above cleaning solutions for at least one minute.

Dilute seawater such as found in whitebaiting areas is ineffective at killing didymo. Whitebaiters who prefer to decontaminate their gear with salt should use a 2% by volume salt solution (saltier than seawater) prepared by adding one small cup (200 mls) of table salt to water to make 10 litres. Soak for as long as it takes to thoroughly saturate the item, plus for at least an additional ten minutes.

Other options for decontaminating gear include soaking in hot water kept above 45 °C for at least 20 minutes (longer for absorbent items), freezing until solid or drying. Although drying will kill didymo, slightly moist didymo can live for months. To ensure didymo cells are dead by drying, the entire item must be completely dry to the touch, inside and out, then left dry for at least 48 hours before use.

If cleaning or drying is not practical, whitebaiters must restrict their gear to a single waterway.

Whitebait factsheet Link to PDF document (591 KB)
Fish, eels and other aquatic species All fish, eels, whitebait, water cress and other aquatic species should be drained of all surplus water before leaving the bank of the waterway and transported in a watertight container to prevent spillage or contamination of other gear. Cooking, washing in a 5% salt solution for one minute, or freezing until solid will kill any didymo present.

Prevent untreated water from entering storm drains. Do not dispose of water, fish or other aquatic species into another waterway.
Jet boats jet skis, and outboard motor boats All boats and trailers should be cleaned thoroughly both inside and out for at least one minute with decontamination solution.

In addition, special attention should be given to the following components:

Jet boat grate: Manually remove visible clumps of algae from the grate and flush the system with a decontamination solution.

Jet unit: Open ball valve at bottom of sand trap, remove any residue and flush system with a decontamination solution.

Outboard motor: The cooling system should be flushed out with the decontamination solution for the specified time. It may then be flushed again with clean fresh water that has come from a town water supply.

Boat interior including anchor recess: Remove excessive water by removing bungs and then wash interior with a decontamination solution.

Bilge pump: Flush interior of boat with a decontamination solution and then use the bilge pump to expel residual water before bungs are opened. This ensures that the bilge pump is flushed with the solution, and that residual water within the pump will be free of live didymo cells.

Mats, carpet (including carpet on the trailer), anchor rope and other absorbent components: thoroughly soak with decontamination solution allowing extra time for the solution to fully soak through the item.

Drying is an acceptable alternative method, provided that all components are completely dry to the touch, inside and out, and then left dry for at least another 48 hours before entering a different waterway.

If you do not want to decontaminate your gear, you should restrict use to a single waterway.
Other watercraft Kayaks, canoes, dinghies and associated equipment and gear should be cleaned thoroughly both inside and out with a decontamination solution. Scrub or spray all exterior parts of the craft with a decontamination solution, ensuring surface contact for at least one minute. Then fill the interior of the craft with the decontamination solution, place all associated equipment, gear and clothing used in the boating activity into the craft, immerse completely and soak for as long as needed to thoroughly penetrate all absorbent items.

The equipment may then be rinsed using water that has come from a town water supply.

Drying is an acceptable alternative method, provided that all components are completely dry to the touch, inside and out, and then left dry for at least another 48 hours before entering a different waterway.

Freezing small items is another option.

If you do not want to decontaminate your gear, you should restrict use to a single waterway.
Vehicles Vehicles should be cleaned thoroughly with a decontamination solution, including spraying the underside of the vehicle and any other parts of the vehicle that have had contact with river or lake water. Commercial carwashes with an underside spray would be suitable. For tyres, see the following tyre section.

The decontamination solution should be left on for at least one minute and may then be rinsed off with water that has come from a town water supply.

Drying is an acceptable alternative method, provided that all components are completely dry to the touch, inside and out, and then left dry for at least another 48 hours before entering a different waterway.

If you do not want to decontaminate your gear, you should restrict use to a single waterway.
Tyres Tyres which have been backed into streams or used for stream crossings must be carefully checked for clumps of algae and other debris within the treads and then scrubbed, soaked or sprayed and flushed with a cleaning solution for the required treatment time. Tyres may then be rinsed using water that has come from a town water supply.

Drying is an acceptable alternative method, provided that all components are completely dry to the touch, inside and out, and then left dry for at least another 48 hours before entering a different waterway.

If you do not want to decontaminate your gear, you should restrict use to a single waterway.
People Swimmers and other water users should wash with soap or shampoo before entering another waterway. Alternatively, ensure hair and skin is thoroughly dry before entering another waterway.
Clothing, Shoes and Toys All wet equipment, toys, clothing and footwear, such as swim wear, beach balls and tramping shoes and socks, should be checked for clumps of algae and other debris, then cleaned with a decontamination solution. Allow longer time for absorbent items, such as clothing, towels and boots. Pay particular attention to the soles of tramping boots and other footwear with a deep tread. Laundry detergent is an effective option for towels and clothing.

After treatment, items may then be rinsed with water that has come from a town water supply.

Drying is an acceptable alternative method, provided that all components are completely dry to the touch, inside and out, and then left dry for at least another 48 hours before entering a different waterway. Alternatively, freeze items until solid.

If you do not want to decontaminate your gear, you should restrict use to a single waterway.
Machinery Machinery (e.g., pumps, hoses, tanks, spray units) should be scrubbed, soaked, sprayed or flushed with a decontamination solution, ensuring that there is a contact time of at least one minute.

Equipment may then be rinsed using water that has come from a town water supply.

Drying is an acceptable alternative method, provided that all components are completely dry to the touch, inside and out, and then left dry for at least another 48 hours before entering a different waterway. Give particular attention to components where water might pool, such as sections of pipes and inside tanks and spillage trays.

If you do not want to decontaminate your gear, you should restrict use to a single waterway.
Farm animals Farm animals (including dogs) should be held or contained in an area away from waterways for not less than 48 hours after they are thoroughly dry, before moved near another waterway.
Pets Pets should be soaked, and then washed for not less than one minute with a suitable animal disinfectant or shampoo. They may then be rinsed using water that has come from a town water supply.

Alternatively, thoroughly dry your pets then contain for not less than 48 hours before they are allowed into another waterway.
Gravel extraction and other riverbed material Earth, stones, boulders, shingle, metal, minerals, gravel, silt and sand should be extracted and piled on high ground near to where they were extracted and be left to drain back into the waterway. Prevent drainage in a new waterway.

Do not transport to a new waterway, or where runoff could flow into a new waterway, until the consignment has been thoroughly dry for at least 48 hours.