Skip to main content

The charity making life better by water

Tackling invasive plant species

Invasive plant species can cause devastation to native flora, fauna and canal ecosystems with their dominating presence and rapid growth.

A moorhen and two chicks peck at green water fern covering the surface of the canal

Why are invasive plant species a problem?

Invasive plant species overpower other native plants and wildlife, and destroy precious habitats. They can block canals, forming thick green carpets which restricts navigation and damages boats.

Every year it costs us hundreds of thousands of pounds to clear away unwanted vegetation and manage the delicate ecosystems which exist in many of our waterways.

What harmful plants do we need to watch out for?

The warmer summer months encourage non-native plant species to grow at alarming speed. Keep your eyes peeled for some of the major hitters, and know what to do if you come across any.

1. Giant hogweed

Heracleum mantegazzianum

Appearance: Whilst growing, giant hogweed is similar to cow parsley and our native common hogweed, but at full height it is much larger and easily distinguishable.

It has sharply serrated leaves, which can grow up to three metres long and have bristles on the underside. The plant stems can grow up to five meters tall and 10cm wide, and are also usually covered with sharp bristles.

The flowers, which can stretch to 80cm in width, are white and umbrella shaped.

Problems: The size of giant hogweed means other plants are left without sunlight, which, when it dies off in the winter, results in bare waterway banks void of vegetation. This in turn increases the risk of erosion, and reduces suitable habitat space for a variety of wildlife, including the endangered water vole.

Controlling its spread is challenging; its huge flowers can hold as many as 50,000 seeds which float down waterways and enable it to grow elsewhere.

It is also harmful to humans. Coming into contact with this plant can burn skin and cause serious lifelong issues when exposed to sun. This means it can only be treated by qualified, suitably protected contractors.

Location: Usually near larger riverbanks, but can be found near any stretch of water. Widespread across the UK

2. Japanese knotweed

Fallopia japonica

Appearance: Japanese knotweed grows vertically in dense thickets. It has bamboo-like stems, which are speckled purple and green, whilst its leaves are 'shield-shaped', and grow off zig-zagging stems.

Problems: The weed has no natural predators, enabling it to grow up two centimetres a day, and three metres high overall.

Its density dominates areas, smothering other native plants and eroding waterway banks. It can also grow through tarmac and concrete, breaking the surface open, which can cause serious damage to our structures.

Japanese knotweed can't be cut or manually removed due to its ability to grow from fragments smaller than a one pence piece. It either has to be mechanically removed by specialist contractors, which requires strict biosecurity and is very expensive, or sprayed with herbicide - a slower, yet still costly, process.

Location: Usually on bank structures/habitats including towpaths, cuttings and embankments. Widespread across the UK.

3. Floating pennywort

Hydrocotyle ranunculoides

Appearance: Floating pennywort has a distinctive bright green, kidney-shaped leaf with crinkled edges. They are usually quite shiny and grow to around 7cm wide. This invasive species is often seen in thick, dense mats across long stretches of water.

Between July and August, tiny white flowers can also appear, although this is uncommon.

Problems: In the warmer months, floating pennywort can grow up to 20cm a day. Its dominating presence steals sunlight, smothers habitats and crowds out native plants. Its excessive coverage on the surface of water can impede flow, causing oxygen depletion for fish and other organisms. Boaters and other craft users can face major problems from its long, fleshy stems tangling in propellers and oars.

When it dies back in the winter, it can cause excessive nutrients to build up in the water and damage ecosystems.

Floating pennywort has the ability to grow from minuscule fragments, making its removal incredibly difficult and expensive. We use specialist machinery to rid canals of large quantities, and our volunteers remove smaller pieces from the water by hand.

Location: Typically seen on the surface of the water, more prominent in the south-east of England, and north-west of England and Wales.

4. Water Fern

Azolla filiculoides

Appearance: Water fern (also known as Azolla) has tiny leaves, only about 2.5cm long. Usually green in appearance, they can sometimes have a reddish tint, and turn completely red in cold weather or shady environments. Below these rough-looking leaves are dark brown, almost black roots, which break easily.

Problems: Water fern forms dense mats on the surface of the water, and can double its area in just a few days.

Able to grow in any depth of water, it reduces light beneath the surface and shades out other native plants. This in turn results in de-oxygenation, suffocating fish and other aquatic species.

The texture of water fern can appear solid to walk on, which also poses a safety hazard.

Location: In still or slow moving water. More prominent in southern and central England, but can also be found in Yorkshire and Wales.

How to report invasive species

If you see an invasive, non-native plant species on one of our canals or rivers, please contact us online or call us on 0303 040 4040 and we'll check if it is already included in our treatment schedule.

How you can help prevent the spread of invasive species

Whether you use our canals and rivers for work or pleasure, please remember to Check, Clean, Dry.

These three things should always be done before you leave a waterway, even if you are moving to another spot on the same stretch just a few miles away.

Check any clothing, tools or equipment that have come into contact with the water, or mud nearby. Even the tread on your bike or the fur of your dog might be carrying an invasive species. If you find any plant fragments or animals, remove them and leave them at the site. Ideally, bin them, but always make sure they can't get back into the water.

Clean your clothing, tools or equipment. Ideally with hot water, but a good rinse with clean cold water will also dislodge bits of plants and young animals that you can't see. Use a bottle of fresh water if you have one handy, or wash things down with a hose. Try and do it on a surface where the water can drain into the ground.

Dry everything completely. Preferably in the sun, leaving no damp patches. Don't forget about items like wet suits, waders and boots. Small invertebrates can live for days in damp folds in clothing and seeds can get stuck in the tread of muddy boots.

  • Read the video transcript

    So, here we are on the River Weaver in Cheshire. And we’re here to talk about invasive non-native species and how we can all prevent them spreading through a process called ‘check, clean, dry’.

    So on the river, we have a real big problem with floating pennywort. And at the moment, the river’s clear. But in summer in late summer, it can completely cover the waterway.

    More than 50 non-native species have accidentally been introduced into our canals, rivers, and lakes from all over the world. And numbers are rising rapidly. They can cause major damage. They outcompete native wildlife, damage ecosystems, and spread disease. They can also block canals, causing a thick, green carpet, which restricts navigation, clogs up propellers, and damages boats.

    The Canal & River Trust is a charity, and every year, it costs us hundreds of thousands of pounds to clear unwanted vegetation and manage the delicate ecosystems which exist in many of our waterways.

    So, what harmful plants and animals do we need to watch out for? So, we’re talking about things like Japanese knotweed and giant hogweed, but also things that you might not see, freshwater shrimp or zebra and quagga mussels. Quagga mussels have even been found in an isolated angling reservoir in Lincolnshire. The nearest other known place with quagga mussels is London, which is over 140 miles away. So, how did this species travel overland for such a long distance? It probably hitchhiked on a person, on their equipment, tools, or machinery. Some species can survive for days, even up to a week, in a damp environment.

    So, how can people help? One of the most important things everyone can do is to stop the spread of harmful plants and animals to a new area. There are three simple steps to remember: check, clean, dry. This should be done before you leave a waterway, even if you’re only moving to another spot on the same waterway but a few miles away.

    The first step is to check any clothing, tools, or equipment have come into contact with the water – or even mud around the water. If you find any plant fragments or animals, remove them and leave them at the site. Ideally, bin them, but always make sure that they can’t get back into the water.

    The second step is to clean your clothing, tools, or equipment, ideally with hot water, but real good rinse with cold water will also dislodge bits of plants and young animals that you cannot see. Use a bottle of fresh water if you have one, or wash things down with a hose. Try and do it on a surface where the water can drain into the ground.

    The last step is to dry everything completely, ideally in the sun, leaving no damp patches.

    Don’t forget about clothes as well, things like wetsuits, waders on boots. Small invertebrates can live for days in damp folds and clothing, and seeds can get stuck in the tread of muddy boots.

    We’re here to talk about invasive species. Where would you check on your boat for invasive species?

    The most obvious places would be the weed hatch, the front and back fenders, mooring lines front and back and centre, anything that’s going to be touching the water, so boat poles, any cans or dippers that you might be using, anything that’s really making contact with the water. If you get anything around the propeller, then obviously you go into the weed hatch, and you have to get your arm in there and clear it. The most important thing then would obviously be to try and remove that, whatever you get. If it’s something like pennywort or something like that, to try and remove it from the canal.

    So, how regularly would you check and clean your boat?

    Okay, so if you’re going on a long journey, I would say that you need to do it at the start of the journey, and as frequently as possible really, preferably once a day. If you’re going from one waterway to another, then I would say so definitely do it. If you’re going from a river to a canal, then you might be transferring things from a river that don’t belong on a canal and vice versa, really. Things will dry off quite naturally in the open air, and there’s plenty of it out here really. But anything that you can dry off, you could do it like a car really with like a chamois leather or things like that, or you could think about having like a fresh set of ropes in a locker so every couple of days you could swap and change your ropes over after you’ve cleaned and dried them.

    So, where would weed or invasive species get caught on your boat, and how do you go about checking and cleaning it?

    We’ll get it caught in various places, like the riggers, the fin, the bowel ball at the bottom. If you capsize, you may get it in here as well. Going about cleaning it, would get a hot water and some sponge, give it a once over and try and get rid of every last bit of dirt.

    Where does weed or invasive species tend to get caught on a paddleboard?

    Well, Tom, they get caught in the very front on the valve seating, and as we come down to the board, you can see it gets caught in the luggage bungee cords here, and then, of course, as you come down to the footplate, you can see it gets embedded into the non-slip surface of the spot plate. And again, on the leash, you can see on the velcro on the leash, it really does capture it, you know, so it needs to be cleaned thoroughly and as we go further down onto the leash onto the D-ring it gets caught there. And, of course, if you turn the board over, you can see the fin at the back, it tends to get captured into the fin as well and the securing nook. And then finally, on your paddle. You get spores on the paddle as well, so of course, when you take it home, you must ensure you wash it clean with fully cold water. And any weed that you collect from your board is disposed of in a nearby bin or left on the land but not put back in the water.

    So, where is most important to check for invasive species in all your equipment?

    Okay, well, if you’re a canal angler, you’re on the towpath, actually, your box and equipment on the towpath isn’t actually as high risk. It’s the stuff that’s in the water where you need to check first, so you’ve got your landing nets, which you check looking for if anything that hits the ride and also if you’re a match angler and some pleasure anglers use these too, these are called keep nets, and this is where you put your catch in, and at the end of the session, you can see what you’ve caught. So, taking a keep net out, we will do, just as before, we’ll do a quick check to make sure there’s nothing in there. We shall tip it out. And look at there, straight away, we’ve got some plants that have sneaked in.

    So, we’ve all got a role to play to prevent invasive non-native species from spreading around. Remember the three simple steps of check, clean, dry – especially when you’re going to different waterways. Please help us to help the waterways we all love to stay special.

  • Read the video transcript (Invasive species control: contractors)

    Here we are on the River Weaver, working with our framework contractor Land & Water Services, to dredge the canal for navigation, and we’ve come here today to talk about how when we carry out works on the waterway, we need to implement biosecurity measures to make sure that we’re not spreading invasive species.

    More than 50 non-native species have accidentally been introduced into our canals, rivers, and lakes from all over the world. And numbers are rising rapidly. They can cause major damage. They outcompete native wildlife, damage ecosystems, and spread disease. They can also block canals, causing a thick, green carpet, which restricts navigation, clogs up propellers, and damages boats.

    The Canal & River Trust is a charity, and every year, it costs us hundreds of thousands of pounds to clear unwanted vegetation and manage the delicate ecosystems which exist in many of our waterways.

    So, what harmful plants and animals do we need to watch out for? So, we’re talking about things like Japanese knotweed and giant hogweed, but also things that you might not see, freshwater shrimp or zebra and quagga mussels. Quagga mussels have even been found in an isolated angling reservoir in Lincolnshire. The nearest other known place with quagga mussels is London, which is over 140 miles away. So, how did this species travel overland for such a long distance? It probably hitchhiked on a person, on their equipment, tools, or machinery. Some species can survive for days, even up to a week, in a damp environment.

    So, how can people help? One of the most important things everyone can do is to stop the spread of harmful plants and animals to a new area. There are three simple steps to remember: check, clean, dry. This should be done before you leave a waterway, even if you’re only moving to another spot on the same waterway but a few miles away.

    The first step is to check any clothing, tools, or equipment have come into contact with the water – or even mud around the water. If you find any plant fragments or animals, remove them and leave them at the site. Ideally, bin them, but always make sure that they can’t get back into the water.

    The second step is to clean your clothing, tools, or equipment, ideally with hot water, but real good rinse with cold water will also dislodge bits of plants and young animals that you cannot see. Use a bottle of fresh water if you have one, or wash things down with a hose. Try and do it on a surface where the water can drain into the ground.

    The last step is to dry everything completely, ideally in the sun, leaving no damp patches.

    Don’t forget about clothes as well, things like wetsuits, waders on boots. Small invertebrates can live for days in damp folds and clothing, and seeds can get stuck in the tread of muddy boots.

    So, Peter, we’re here with Land & Water Services to talk about invasive species, but what do they need to think about for check, clean, dry?

    Well, so the first thing to start with is all this big plant isn’t it? So, we’ve got diggers, we’ve got dumpers, we’ve got all kinds of vehicles here, and it’s all kit that will go from site to site. So, really, they need to make sure that when they bring it to a new site like this that it’s clean before it gets here. Check to see whether there’s any obvious mud or plant material or other stuff on the vehicle, particularly in the tracks or the bucket or anything that might have been in the mud or the water. If there is stuff, clean it off. A jet wash is fantastic on these kinds of big bits of kit. And then, if you’re moving stuff away to another site, make sure it’s dry before it goes somewhere else and then you can be sure that you’ve got rid of everything.

    So, what about smaller stuff like tools and equipment?

    Yeah, right, so obviously, on a lot of our jobs, people are using small kit like shovels and so on, and that’s just as important because as you can see from the state of this spade, yeah, there’s mud there that I might be transferring from one job to another. Now, if you’re on the same job for a long period of time, obviously you don’t need to worry about that. The kit’s not going anywhere. But if you’re on a more reactive team and you’re moving from one site to another in the same day, then clearly, we don’t want to be tracking this mud from the River Weaver up onto the Trent & Mersey or the Shropshire Union or somewhere else. So, it’s really important that again you check it and clean it, and if you can, dry it before you leave site.

    Another area that potentially we need to think about is your clothing, like your boots and anything like waders or anything. What about check, clean, dry with those sorts of things?

    Yeah, absolutely, Tom. So, a lot of our work is really mucky, so yeah, we are going to get covered in mud from doing works on the waterways, and so it’s very easy for us to transfer plants and materials from one site to another if we don’t clean ourselves as we go.

    Now, I’m not terribly muddy today, but I have got some mud on me boots there. And we don’t want to be tracing that off to another site. So, just check it to see if there’s anything on it that needs removing. Clean off what you can with water and with a brush, and then make sure that you dry it out if you can.

    So, what’s the risk about moving soil around and preventing invasive species being spread like that?

    Well, obviously, if you know you’ve got Japanese knotweed or Himalayan balsam or something like that on the site, then when you start excavating in this area, we don’t want to be picking any of that material up and moving it off-site because that would be spreading those invasive plants.

    We ask everyone to play their part. Please help us help keep our waterways, which we all love, special.

  • Read the video transcript (Invasive species control: boat hire)

    So, here we are today at Aqueduct Marina in Cheshire and we’re here to talk about how we can clean a boat that’s been taken out of the water, and that’s really important for maintenance, but also the really key thing is when a boat is being taken a long distance over land. And we’re here to look at how a boat should be cleaned to prevent the spread of invasive non-native species.

    More than 50 non-native species have accidentally been introduced into our canals, rivers, and lakes from all over the world. And numbers are rising rapidly. They can cause major damage. They outcompete native wildlife, damage ecosystems, and spread disease. They can also block canals, causing a thick, green carpet, which restricts navigation, clogs up propellers, and damages boats.

    The Canal & River Trust is a charity, and every year, it costs us hundreds of thousands of pounds to clear unwanted vegetation and manage the delicate ecosystems which exist in many of our waterways.

    So, what harmful plants and animals do we need to watch out for? So, we’re talking about things like Japanese knotweed and giant hogweed, but also things that you might not see, freshwater shrimp or zebra and quagga mussels. Quagga mussels have even been found in an isolated angling reservoir in Lincolnshire. The nearest other known place with quagga mussels is London, which is over 140 miles away. So, how did this species travel overland for such a long distance? It probably hitchhiked on a person, on their equipment, tools, or machinery. Some species can survive for days, even up to a week, in a damp environment.

    So, how can people help? One of the most important things everyone can do is to stop the spread of harmful plants and animals to a new area. There are three simple steps to remember: check, clean, dry. This should be done before you leave a waterway, even if you’re only moving to another spot on the same waterway but a few miles away.

    The first step is to check any clothing, tools, or equipment have come into contact with the water – or even mud around the water. If you find any plant fragments or animals, remove them and leave them at the site. Ideally, bin them, but always make sure that they can’t get back into the water.

    The second step is to clean your clothing, tools, or equipment, ideally with hot water, but real good rinse with cold water will also dislodge bits of plants and young animals that you cannot see. Use a bottle of fresh water if you have one, or wash things down with a hose. Try and do it on a surface where the water can drain into the ground.

    The last step is to dry everything completely, ideally in the sun, leaving no damp patches.

    Don’t forget about clothes as well, things like wetsuits, waders on boots. Small invertebrates can live for days in damp folds and clothing, and seeds can get stuck in the tread of muddy boots.

    So, when we’ve got our boats out, this is a really good set-up. It’s far enough away from the water, so anything washed off doesn’t end up back in the water course. It’s also a built environment, so all the invasive species that washed off get captured. There are then drains, so the wastewater gets captured as well, and doesn’t end up in another water course. All of this means that we’re not spreading invasive species to other watercourses. This set-up is also really good because the boat is slightly higher, which means that we can jet wash underneath, and that’s really key because invasive species will still cling there.

    So, the boat’s out of the water and you can quite clearly see how much material, plant material and even zebra mussels, are attached to the boat and that’s why it’s really important when a boat is coming out of the water and it’s being transported to somewhere else across land, or even just for maintenance, that the boat is really thoroughly cleaned. That check, clean, dry is really important when a boat is out of the water.

    We ask everyone to play their part. Please help us to help the waterways we all love to stay special.

Last Edited: 20 March 2025

photo of a location on the canals
newsletter logo

Stay connected

Sign up to our monthly newsletter and be the first to hear about campaigns, upcoming events and fundraising inspiration