Check, Clean, Dry: preventing didymo and other pests

Freshwater pests can be spread by your activities in and around waterways. If you're moving between waterways, you must clean all your gear using the 'Check, Clean, Dry' method. Learn how to check, clean, dry your gear.

Clean all gear when moving between waterways

Freshwater pests, including didymo, could squeeze the life out of our country's most precious rivers and lakes. They can be spread by a single drop of water or plant fragment. You can help to protect your favourite waterways if you always check, clean, then dry any equipment that comes into contact with the water, between every waterway, every time.

The South Island is a controlled area

The South Island is a controlled area for didymo. This makes it a legal requirement to clean all gear used in the water before going from one waterway to another.

So far, no didymo has been found in the North Island but it is good practice to check, clean, and dry when you move between waterways.

The Check, Clean, Dry method

To prevent the spread of freshwater pests (like didymo), whenever you move between waterways you must check, clean and dry all your gear that comes into contact with water. If you don't want to treat your gear, make sure you only use it in one waterway.


Remove any plant matter from your gear and leave it at the site (the river or lake bank), or put it in the rubbish. Don't wash plant material down any drain.


There's more than one option for cleaning your gear – choose the one that's best for your situation and your gear.

Cleaning options

OptionAmountTreatment time2
Dishwashing detergent or nappy cleaner 5% solution
(500mls diluted to 10 litres in water)
Soak or spray all surfaces for at least 1 minute
Bleach 2% solution
(200mls diluted to 10 litres in water)
Soak or spray all surfaces for at least 1 minute
Hot water1

Above 60°C

Above 45°C

Soak for at least 1 minute

Soak for at least 20 minutes

Freezing   Until solid

1 60°C – hotter than most tap water; 45°C – uncomfortable to touch

2 Allow longer times for absorbent items.

Cleaning large volumes of gear

If you have large amounts of gear (for example if you have a fishing or diving business), you can find other suitable options in Appendix 3 of Check, Clean, Dry: Information for sporting event organisers.

Make sure you:

  • follow the manufacturer's safety instructions for any cleaning products
  • choose a method that won't damage your gear
  • check the cleaning solution has penetrated right through the item before you soak it for the recommended time
  • check our cleaning instructions for specific items – some have different cleaning requirements.


Ensure your gear is completely dry to touch, inside and out, then leave dry for at least another 48 hours before you use it (didymo can survive for months on moist gear).

Video – How to clean your gear (7:53)

MAF Didymo Programme Manager John Sanson and another man named Lance are at a lake, preparing to tow a boat behind a truck.

John: New Zealand has some of the most beautiful rivers and lakes in the world, and we need your help to keep them that way.

Lance: One way that freshwater pests can be transferred between waterways is on recreational items that you use in the water - everything from boats to boots. And once these pests are in the water they can have a detrimental effect on wildlife in our rivers and lakes and the quality of the recreational experience our waterways offer.

John: Because it only takes one pair of tramping boots or a wet lifejacket to give a hitchhiking freshwater pest a ride to a new location where it can establish and cause damage.

[Card: Protect our fresh waterways from pests. Check, clean, dry - everywhere, everytime.]

Lance: Now John deals with pest species in our waterways, and he's seen some of the harm they can cause. Now we're talking about didymo or what some people call rock snot, aren't we?

John: Not just didymo, Lance. That's had a high profile in recent years, but there are plenty of other pests invading our fresh waterways.

[Underwater video of each pest is shown as John describes it.)

Lagarosiphon is a fast-growing freshwater weed. Grows up to 5 meters tall forming dense mats which block waterways and displace native plants. It's a major problem in hydroelectric dams, and can block irrigation and drainage systems.

Hornwort is found in still and flowing waters growing to depths of 16 meters in clear, deep lakes. New plants can form from each piece of the easily broken stems and its dense growth crowds out native species.

Hydrilla is an oxygen weed. They can grow up to 9 meters tall in still or slow flowing freshwater. It's spread mainly through stem fragments which are easily transported to other waterways by machinery, boats, trailers or nets. At present it's only found in 4 Hawke's Bay lakes, but once established is virtually impossible to get rid of, once again forming dense mats which clog waterways.

And of course as we mentioned at the start there's our most invasive algal - didymo. In bloom it forms thick brown mats that smother rocks, submerged plants and other materials. It can clog irrigation and hydroelectric systems, and frankly it's an unsightly mess that can seriously harm the enjoyment of activities such as fishing and boating.

Lance: Now that's just a few of the main pest species we're up against. But where they do establish, everyone has a part to play in ensuring they don't spread, spoiling our fishing, our swimming, our tramping - anything that people enjoy doing on the water.

But if someone's out and about traveling between different waterways how do they know which ones have pests and which haven't?

John: Sometimes it's impossible to tell just by looking. So the best idea is: simply to treat all water you've just left as if it does have pests, and all water you're entering as if it doesn't.

[Card: Treat all water you've just LEFT as if it DOES have Pests, and all water you're ENTERING as if it DOESN'T.]

Lance: A nice simple rule of thumb, and it's pretty simple to remember what to do after you've left the water too.

John: Yup. The Check, Clean, Dry programme was established when it was realised just how quickly didymo was spreading. And it's still the easiest and most effective way for anyone to stop didymo and other freshwater pests in their tracks.

[The Check, Clean, Dry - Everywhere, Everytime logo is seen over video of people jetboating, kayaking, fishing, and hiking.]

[John and Lance are seen looking over the boat and all its gear, including the anchor and chain, propeller, fishing rod, and tow hook-up, and throwing away plant material they find.]

Lance: Ok - so first up - before you leave a river or lake check anything that's been in the water - your boat, fishing gear, vehicle, boat trailer, boots - anything - and remove and leave any debris at the site - not back in the water or down the drain. That's not going to help.

But hold on. If we're talking about things too small to see, how can we check for those?

John: Well no we can't. We're just starting by removing anything we can see which could be a pest or harbor microscopic pests like didymo.

Lance: And are there any things that need particular attention?

John: The underside of vehicles and tyre wells are one, inside your boat or kayak, swimwear and towels, and water toys like lie-lows or inflatable dinghies.

[Lance and John look in a wheel well of the truck, feel around the inside of the boat, and shake out a towel.]

Lance: Alright, you've checked and you've removed any obvious visible debris from your equipment, your vehicle, your clothing.

Now you clean it, and you can do that here or at home. Just so long as it's clean before using another waterway. And we're not just talking a hose-down with water, are we?

[John brings a bucket, bottle of dish detergent, scrub brush, sponge, and measuring cup.]

John: No, that's right. Water by itself won't kill pests.

Cleaning must be done with a solution of water and 5% of a suitable cleaner like dishwashing liquid, salt, nappy cleaner or antiseptic hand cleaner. These are all items that can be found at your local supermarket or your home.

[John measures out 2 cups of the dish detergent.]

Now a 5% mixture is 500ml or 2 cups of the cleaner with water added to make 10 litres.

Lance: And how accurate do you need to be?

John: As long as the mixture is at least 5% cleaning solution that's all you need to worry about. You can't overdo it when it comes to the effectiveness of the solution.

Lance: So if in doubt, err on the side of caution.

John: That's correct. And we also need to think about the environment. So we recommend using biodegradable cleaning products wherever possible. And it's also important to make sure that your wastewater doesn't dump directly into a drain that leads to a waterway, or a waterway itself.

Lance: All items that have been in contact with the water have to be thoroughly cleaned, and there are several ways to kill didymo. So it's a matter of choosing the most practical treatment for your situation, as well as one that won't adversely affect your gear.

[Lance and John clean various equipment. A lifejacket is shown being submerged in a bucket of sudsy water. Lance sprays cleaner on the reel of a fishing rod and wipes it with a dry cloth. A coiled rope is submerged in a bucket of sudsy water. John sprays cleaner on the tire of the boat trailer and inside the wheel well. A sudsy scrub brush is used on the side of the boat. John scrubs the bottoms of waders with a brush before submerging them completely in a bucket of sudsy water.]

John: Hard surfaces can be sprayed and scrubbed with the solution, while absorbent items like ropes, mats, life jackets and boots should be soaked and scrubbed, all for at least one minute.

Lance: Cleaning the inside of vessels is almost more important than cleaning the outside. Don't neglect areas like carpets and mats, bilges and anchor ropes.

John: And just as importantly, you must clean boots, life jackets, water toys or other gear. And remember - anything that's been in the water must be cleaned.

Lance: Now you might think it's not practical to be carrying cleaning solution around with you if you're out, say, tramping and need to clean your boots. Obviously you're not going to have a hose and bucket with you.

John: Well no. But you could carry a plastic bag with sufficient cleaning solution already in it and simply add the required amount of water from the waterway to clean your boots in.

[A boot is submerged in a plastic zipper bag with soapy water. The bag is closed and swished around to cover and fill the boot with the solution.]

Lance: You'll have to leave any rinsing off until you enter the next waterway where the cleaning solution will wash off. Don't rinse your gear in the water where you've just left.

Now there will be times when cleaning just isn't practical. So the next important step is drying.

[John dries the inside of a kayak with a towel. Lance dries the reel of a fishing rod with a cloth. John runs his hands over the kayak, straps and paddles to make sure they're dry.]

John: Drying alone will kill didymo, but even slightly moist didymo can survive for months. So to ensure the didymo cells are dead by drying, an item must be completely dry to the touch inside and out and left to dry for at least another 48 hours before using back in the water.

Lance: Planning your trip carefully could also help you avoid spreading freshwater pests. For example using only one waterway per weekend will enable enough time between trips for most of your equipment to be completely dry.

However you will have to clean anything made from absorbent material, like life jackets and boat carpets.

John: That's the minimum requirements for protecting our lakes and rivers from the spread of freshwater pests.

Lance: Yeah, it's not comprehensive and there's more info on the MAF Biosecurity New Zealand website, including more specific cleaning instructions for everything from gravel extractors to whitebait nets. Even pets.

John: Ideally you'll check, clean, dry every time you leave a river or lake - a bit like putting on your seatbelt every time you drive.

[Lance and John get in the truck and put on their seatbelts.]

Lance: And by ensuring you check, clean, and dry when you move between waterways you're playing a valuable role in protecting our rivers and lakes now and for future generations.

[The truck drives away.]

End title: MAF Biosecurity New Zealand logo. New Zealand. It's our place to protect.

Thanks to:
Environment Bay of Plenty
Fish & Game New Zealand
Ian Gear

The Check, Clean, Dry programme is a partnership between the Department of Conservation, regional councils, industry, iwi and the community.

[End of transcript]

Treatment by drying

Drying can be used as stand-alone treatment for non-absorbent items if you take great care to:

  • make sure gear is completely dry to touch, inside and out
  • leave dry for at least another 48 hours (after drying), before entering a different waterway.

Cleaning specific items

Most items can be cleaned using the standard Check, Clean, Dry method, but some have additional requirements.

Expand All
Absorbent items including clothing

Absorbent items such as fishing nets, swim wear, clothing, shoes, and toys need to be treated for longer than normal.

Note: Fishing footwear with absorbent material, such as felt-soled waders and boots, carry a high risk of didymo transfer. For this reason you're not allowed to use that type of footwear for freshwater fishing in New Zealand.


Check for and remove clumps of algae and other debris from your gear. Take particular care with the soles of tramping boots and other shoes.


Clean the items with a treatment solution (from the cleaning options table), by drying, or by freezing solid.

If you use a solution, make sure it has penetrated right through the item before you soak it for the recommended time. Laundry detergent can be used to clean towels and clothing.

After treatment, rinse the item with water from a town water supply.


Ensure your gear is completely dry to touch, inside and out, then leave dry for at least another 48 hours before you use it.

Treatment by drying alone

  • Drying alone should only be used if you take care to completely dry the material (for example, by using a heat source).
  • Where gear is frequently used between waterways (daily, weekly or monthly) don't rely on air drying alone.
Fish and other aquatic species

All fish (including eels and whitebait), watercress, and other aquatic species should be:

  • drained of all water before you move them from the bank of the waterway
  • transported in a watertight container to prevent spillage or contamination of other gear
  • cooked, washed in a 5% salt solution for one minute, or frozen solid.

Don't let water or aquatic species get into another waterway, and don't let untreated water get into storm drains.

Fishing equipment

Freshwater fishing equipment

Freshwater fishing gear can be treated with a cleaning solution (from the cleaning options table), by drying, or by freezing solid.

Cleaning solution
  • Soak all rods, reels, fishing lines, flies, tackle boxes, nets, clothing and other equipment.
  • Allow longer treatment times for absorbent items (such as nets).
  • After treatment, rinse with water from a town water supply.

Whitebaiting equipment

Absorbent items (such as nets)

Soak in 5% solution of dishwashing liquid or nappy cleaner until saturated, then for at least one more minute.

Non-absorbent items (such as trailers or buckets)

Choose one of the following options:

  • Standard cleaning solution.
  • Treatment by drying.
  • Salt solution: Soak in a 2% salt solution until saturated, then for at least 10 more minutes. Prepare the salt solution by dissolving one small cup (200ml) of table salt with fresh water to make 10 litres.

Download the Check, Clean, Dry for whitebaiters factsheet [PDF, 591 KB]

Fishing gear brought into New Zealand

All freshwater fishing gear brought into New Zealand must be clean and dry. If it isn't, MPI may need to treat it at your expense or take it from you.

Jet boats, jet skis, and outboard motor boats

Treat by drying or use a cleaning solution.

Cleaning solution

Clean boats and trailers thoroughly, both inside and out, for at least one minute with a cleaning solution (from the cleaning options table).

Take particular care with the following:

  • Jet boat grate: Remove visible clumps of algae from the grate and flush the system with solution.
  • Jet unit: Open ball valve at bottom of sand trap, remove any residue and flush system with solution.
  • Outboard motor: Flush the cooling system out with solution. You can then flush it again with town water.
  • Boat interior including anchor recess: Remove bungs to get rid of excess water, then wash the inside with solution.
  • Bilge pump: Flush inside boat with solution, then use the bilge pump to remove before bungs are opened.
  • Absorbent parts such as mats, carpet (including on trailer), anchor rope: Thoroughly soak with solution allowing extra time to fully soak through.

Treat machinery (such as pumps, hoses, tanks and spray units) by drying or use a cleaning solution. Pay attention to parts where water pools, such as pipes, tanks and spillage trays.

People and animals


  • Wash with soap or shampoo before entering another waterway, or
  • Make sure your hair and skin is thoroughly dry before entering another waterway.


  • Soak and then wash pets for one or more minutes with an animal disinfectant or shampoo.
  • After washing, rinse with town water supply.

Alternatively, thoroughly dry your pet then keep it away from water for at least 48 hours before allowing it into another waterway.

Farm animals

Keep farm animals (including dogs) away from water for at least 48 hours after they are thoroughly dry, before moving them near another waterway.

Other watercraft

Treat all kayaks, canoes, dinghies, and related equipment with a treatment solution or by drying.

If you use a cleaning solution:

  • scrub or spray all exterior parts of the craft with treatment solution, for at least one minute
  • fill the inside with solution, and put all associated equipment (gear and clothing) into it
  • immerse equipment completely and soak to saturate any absorbent items
  • rinse after treatment with town water supply.

Didymo and kayakers – Whitewater NZ website


Vehicles and tyres can be cleaned using a treatment solution, by drying, or using a commercial carwash with an underside spray.

If using a treatment solution
  • Carefully check tyre tread for clumps of algae and other debris.
  • Clean the vehicle thoroughly with a treatment solution, leaving it on for at least one minute.
  • Spray the underside of the vehicle and any other parts that have had contact with river or lake water.
  • Rinse off with town water supply.

Find out more

Who to contact

If you have questions about the Check, Clean, Dry method, email

To order Check, Clean, Dry brochures and guides, email

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