Our purpose is to preserve New Zealand's whitewater resources and enhance opportunities to enjoy them safely.

Didymosphenia geminata (Didymo) and kayakers

The spread of the didymo algae is a disaster for kayakers. Strong measures are required to attempt to restrict the spread.

Aquatic pests and Didymo - a real threat to kayaking

Grab the NZRCA Didymo flyer for your vehicle.NZRCA Didymo Flyer, A5 (PDF, 220k).

The finds of Didymo, an invasive fresh-water algae, and a declared unwanted organism under the Biosecurity Act, in several South Island Rivers, has highlighted the threat that aquatic pests may pose and the huge impact they can have (and are already having) on river systems and paddling.

Biosecurity New Zealand has recently declared the whole of the South Island to be a "controlled area" (PDF, 44k). Map of affected areas (JPEG).

What kayakers need to do to protect our rivers - Check, Clean, Dry between every river

Our rivers are not a lost cause despite Didymo already having a firm hold in some areas. We can help by keeping the biomass of known or likely populations of Didymo as low as possible, minimising the ecological effects of the algae.

Didymo on Mararoa River, December 2005

Didymo on Mararoa River, December 2005

Most importantly, this issue is not just about Didymo. Didymo is unlikely to be the last aquatic pest to inadvertently hit our shores - we need to do whatever we can to prevent the spread of other aquatic pests that may enter New Zealand in the future. Keep in mind that some aquatic pests can go undetected for a long time (like Didymo was initially).

The only way we can protect our rivers in the long term is to: Check, Clean, Dry all your kayaking gear before entering another river or lake, anywhere in New Zealand.

Note that if you follow this mantra you are very unlikely to fall foul of the law and knowingly spread a declared unwanted organism - an offence under the Biosecurity Act with some pretty stiff penalties.

Cleaning your gear

Check, Clean, Dry is now part of the New Zealand kayak way of life and you will need to organise your own system for cleaning your kayaking gear (we suggest a simple system using a large plastic bin, the cleaning agent and a sponge) that can be taken with you when required.

Permanent cleaning facilities have also been set up at the New Zealand Kayak School and Riverview Campground in Murchison, the Hawea slalom site, and at Sunspots, Rotorua. You should not expect to rely exclusively on these facilities especially during peak periods (e.g., Christmas / New Year at Murchison) and you will need your own cleaning system when visiting other areas.

Check, Clean, Dry - Recommendations for kayakers

Before entering any other river or lake:

Before leaving the river, remove all obvious clumps of algae and look for hidden clumps. Leave them at the affected site (away from the river). 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.
Mix in 5% of household disinfectant.
  • Put 10 or 20 litres of water in a tub (try the one you carry wet gear in). Disinfectants for didymo
  • Mix in 5% of household disinfectant. 10 litre tub: use 2 large cups (500ml). 20 litre tub: use 4 large cups (1 litre).
  • Drain boats and squeeze water out of wet gear as thoroughly as possible.
  • Soak all gear in the tub for at least a minute, squeeze excess solution back into the tub.
  • Pour remaining solution into kayak, slosh around to wet the entire inside (try to get spillage from cockpit back into the tub or next kayak).
  • Drain from first kayak into the next and so on until insides of all boats are wetted with solution.
  • Use remaining solution to sponge down the outside of kayaks and paddles.
  • Dispose of excess solution well away from river and if you have to rinse gear do so in tap water not the river water.
If possible, leave your boat and gear to dry as an extra precaution. Note that if you don't clean your gear you need to dry all your gear thoroughly and then leave for another 48 hours. Given the difficulty of completely drying wetsuit booties and other kayaking gear, cleaning is preferred.


  • Buy disinfectant from a supermarket for about $2 for a two litre bottle. If you use 500ml it will cost you about 50 cents every time you clean your gear. A small price to pay to protect our rivers!
  • Make a mark with a felt pen on the side of the washing tub to show the required water level for future treatments.
  • It's a good idea to mark 250 ml and 500ml on an old plastic bottle (e.g. clean one litre milk bottle) and use this to measure disinfectant.
  • Report suspected new finds of Didymo to and for more information visit rivers.org.nz/article/Didymo.

Other hints

  • Plan your trip so that you paddle affected or high-risk areas last.
  • Help spread the message, Check, Clean, Dry when moving between any river.
  • Offer the use of your cleaning gear to others if necessary.
  • Take multiple sets of gear

Notes on choice of cleaning agent

Biosecurity New Zealand is quite specific on what cleaning agents are allowed to be used (see http://www.biosecurity.govt.nz/didymo).

While boats and paddles are generally pretty resilient to cleaning, other kayaking gear (e.g., buoyancy aids, spraydecks, drytops and clothing) has to be handled with some care. Investigation by the NZRCA and the Whitewater Canoe Club in Christchurch suggests that the best cleaning option for cleaning your gear is biodegradable laundry or dishwashing detergent. This is least likely to harm your kayaking gear. However, detergent is foamy and slippery and the NZRCA has investigated the use of household disinfectant containing the active ingredient benzalkonium chloride. Biosecurity New Zealand has advised that "Having reviewed this chemical, we consider that Benzalkonium chloride would be covered in the decontamination recommendations for didymo in the antiseptic hand cleaner category."

Salt is often the only feasible solution at fixed cleaning facilities (e.g., NZ Kayak School). It is also another potential option for use by individuals (though disinfectant is better). Use of bleach or nappy cleaner is not recommended due to cost and potential damage to garments.

Regardless of which cleaning solution you use, you will minimise any potential damage to your gear if you rinse it with freshwater (not river water!) after cleaning.

Disclaimer: There are no guarantees - neither the NZRCA, nor the Whitewater Canoe Club take responsibility or are liable for any damage to kayaking equipment caused by following these recommendations.

What do I do if I suspect that Didymo or another aquatic pest is in a waterway?
If you suspect Didymo or another aquatic pest is in other waterways, call the MAF hotline number 66.


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