Didymo, can we help stop it?

Tips for Trampers
December 2007

With summer approaching, the country’s beautiful rivers, lakes and bush are calling, but with this comes the risk of outdoor activities spreading didymo and other aquatic pests and weeds.

 "Rock Snot" Didymo, or ‘rock snot’ is an invasive algae that can be spread through damp equipment, clothing and boots. It was discovered in New Zealand in 2004 and can now be found in many South Island rivers, where it is an unsightly threat to native ecology and poses an economic threat to tourism, hydro-power generation, fisheries, sports fishing and irrigation.

Didymo is spread between waterways only by human movement. Its microscopic cells hitchhike on equipment such as boats, trailers, waders, fishing rods, kayaks, bikes, tramping boots and potentially even on fish taken from the South Island and released in the North.

Once didymo dries out it is neutralised but if wet it is quickly able to establish itself in suitable water and multiply rapidly. In some rivers didymo forms mats 12cm thick.

Didymo has not established itself in the North Island yet, but there have been a number of recent scares and conservation organisations and people working in the field have been placed on ‘high alert’ because the situation could well change at any time.

Trampers can do their bit to keep our North Island rivers didymo-free and to slow the spread in the South Island by following some simple rules: Check, Clean and Dry.

Check

Before leaving a lake or river, check your gear, including your tramping boots and socks, vehicle and tyres and any other equipment used and remove any clumps of algae and debris and look for hidden clumps, as this is where the microscopic didymo cells may be hiding. Pay particular attention to tramping boots with a deep tread, and always decontaminate these too, regardless of whether there is any visible debris. If you find any debris later, don’t put it down the drain. Instead, treat it with one of the methods below, let it dry and put it in the rubbish bin.

Clean

Clean your equipment, vehicle and tyres or clothing with either:
Detergent: soak or spray all surfaces for at least one minute in 5% dishwashing detergent or nappy cleaner (two large cups or 500 mls with water added to make 10 litres). If your vehicle has been in contact with a lake or river, you’ll even need to spray the underside or take it through a carwash that does an underside spray. Or
Bleach: soak or spray all surfaces for at least one minute in 2% household bleach (one small cup or 200 mls 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).
Soak absorbent materials such as felt-soled shoes or boots, for at least 40 minutes in hot water kept above 45°C; or soak for 30 minutes in hot water kept above 45°C containing 5% dishwashing detergent or nappy cleaner.
After treatment, items may then be rinsed with water that has come from a town water supply.

Dry

Drying will kill didymo, but 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 in a different waterway. Slightly moist didymo can survive for months.
To avoid having to decontaminate your gear, restrict equipment to a single waterway.

You can find out more on www.biosecurity.govt.nz or by phoning Amanda Peart, Freshwater Pests Communications Advisor at the Auckland Regional Council on 366 2000 ext 8623