Invasive plants

What are invasive exotic (alien) species (IESs)?

Invasive exotic (alien) species (IES) are plants, animals or micro-organisms (viruses, bacteria, mushrooms, etc.) that have spread beyond their natural range into new areas. Their introduction or propagation can harm the environment, the economy and even society and human health.

How do IESs get here?

Most IESs come into our environment through the ballast water of ships and pleasure boats, through activities like horticulture, aquaculture, aquarium/water-garden trade and through the pet trade. The transportation of organic materials (wood, sand, soil, etc.) can also introduce invasive species into a new area.

This page lists the invasive species found or possibly found in the Val-des-Monts area.

Giant hogweed (Heracleum mantegazzianum)

Giant hogweed is a noxious invasive plant that can be dangerous to humans (burns, scarring). It made its way into Québec in 1990 and continues to spread. If you detect giant hogweed, be sure to take the recommended precautions and to notify both the Municipality and Québec’s ministère de l’Environnement et de la Lutte contre les changements climatiques (MELCC) of its presence.  

How to identify giant hogweed?

  • Height: 2-5 metres
  • Leaves: have three deeply indented/lobed leaflets that can grow three metres long and 1.5 m wide; the underside of the leaf is smooth with no hairs.
  • Flower: forms an upside-down umbrella-shaped head (umbel or cluster) 20 cm to 50 cm in diameter; each umbel can contain between 50 and 150 stocks, and tiny white flowers sprout from each stock. 
  • Stem: Bright green, 4-10 cm, covered in coarse white hairs and reddish-purple spots.  

Giant hogweed usually grows in large colonies bordering cool, wet areas. The plant also populates roadsides, fields and railroads.

Don’t confuse giant hogweed with common cow parsnip, Angelica and Queen Anne’s Lace, three native plants that don’t harm the environment. To learn more, consult the MELCC’s fact sheet on the giant hogweed (in French). For English-language information on the plant, see the Nottawasaga Valley Conservation Authority giant-hogweed fact sheet.


Giant-hogweed sap contains toxins activated by the sun’s rays or by artificial ultraviolet rays. So, if your skin is exposed to these rays once the sap gets onto it, inflammation occurs and produces these symptoms:

  • redness and swelling
  • blisters
  • First-degree burns (superficial) and second-degree burns (more serious).

If giant-hogweed sap gets onto your skin…

Consult the tip sheet titled Burns caused by giant hogweed, published by the Portail santé et mieux-être du gouvernement du Québec.

Help stem the spread of giant hogweed

Please visit these online resources:
Gestion et contrôle de la berce de Caucase (French-language fact sheet by Québec’s MELCC)
Identifying and eliminating giant hogweed, published by the Portail santé et mieux-être du gouvernement du Québec.

More info

Contact Info-Santé at 8-1-1 for health-related questions. If you detect giant hogweed, contact the Municipality of Val-des-Monts at 819-457-9400, and you can also tap into the following resources if you have more questions about giant hogweed:

Water chestnut (Trapa natans)

Water chestnut is an annual aquatic plant that spreads like wildfire in nutrient-rich freshwater lakes and rivers. Originally from Europe and Asia, the plant made its way into Québec in 1998, and it’s now found in many lakes, ponds, marshes and channels. The plant has been observed near Val-des-Monts, specifically in Parc national de Plaisance.

How to identify water chestnut

  • Stem: 1-5 m long; can split into many secondary stems that reach the water’s surface.
  • Leaves: grow in pairs along the stem; form lozenge-shape clusters at the surface (5-8 cm).
  • Flowers: sprout beside the floating leaves; have four white petals and four yellow stamens.
  • Fruit: small (2-4 cm) nut-like fruits with four points.

Environmental impact

Water chestnut grows and spreads lightning fast, easily covering expanses of shallow water. At that point, the plant cover can block up to 95% of the UV rays that normally penetrate deeper into the water. This, in turn, interrupts photosynthesis in underwater plants, which creates a shortage of dissolved oxygen in the water, harming aquatic species that depend on healthy concentrations of oxygen.

Eradicating water chestnut is no easy task given its tenacity and its ability to spread quickly. What’s more, the plant sheds nut-like fruits that sink to the bottom of the water and can stay there 10 to 12 years before germinating, further complicating the fight against water chestnut.

Help stem the spread of water chestnut

  • Inspect and clean watercraft.
  • Know how to identify the plant and prevent its introduction to an area.
  • Pull out the plant with your hands whenever possible.

Common water reed or ditch reed (Phragmites Australis)

Common water reed is a perennial plant originally from Eurasia. Brought to Québec in 1916, it’s now found in wetlands, on roadsides, on waterfronts, in ditches and on vacant lands altered or affected by human activity.

How to identify common water reed

  • Height: up to 4 m (12 feet)
  • Stem: 3-4 m high, 4-10 mm around, hollow greenish or yellowish, non-branching
  • Leaves: green, 1-5 cm, alternating
  • Inflorescence: large cluster of flowers (panicle); 10-18 mm spikelets; 2 mm fruits
  • Roots: dense surface rhizome (less than 85 cm deep) 

Environmental and economic impact

With its ability to spread very fast, the common water reed can upset the environment in many ways; most notably, it reduces biodiversity, overtakes landscapes, impedes horticultural production, and quickly increases the costs linked to its control. And because it causes heavy water evaporation, the plant can dry up wetlands and marshes already vulnerable to desiccation.

The economic impacts are real as well. For instance, because the water reed leaves a thick layer of litter or organic debris on the ground every year (something that could otherwise be perceived as beneficial ecologically), the cost of maintaining ditches increases tremendously.

Help stem the spread of the common water reed

  • Do not plant this invasive species.
  • Immediately plant native species on any bare ground.
  • Plant shade-creating trees and shrubs to stop water reeds from germinating.  
  • Dig down below the rhizomes to pull them out and use non-contaminated soil as backfill.
  • Cut off the plant’s feathery seed heads throughout the flowering season.
  • Cover the affected area with a tarp for at least two years for long-lasting results.

Eurasian water milfoil (Myriophyllum spicatum L.)

Water milfoil is a perennial underwater plant that roots at the bottom of the water. The plant is gaining territory in certain lakes across Val-des-Monts, mostly those with heavy concentrations of vacationers and motorboats.

How to identify Eurasian water milfoil

When “hunting” for the invasive Eurasian water milfoil, be sure not to confuse it with the native northern water milfoil. Consulting this watch card will help. In a nutshell, Eurasian water milfoil has these features:

  • Roots and rhizomes: not deeply anchored.
  • Habitat: found mostly in shallows (1-4 m), but also in deeper water (up to 10 m) if it’s very clear.
  • Stem: submerged, with multiple branching; reaches the surface (up to 6 m).
  • Leaves: green; limbless and feather-like, arranged in whorls around the stem in groups of three or four.
  • Inflorescence: flower clusters standing several inches above the water.[RM1] 
  • Flower: small, three-petalled; creamy white, greenish or purple.
  • Fruit: round.

Economic and environmental impact

Because most lakes invaded by the Eurasian milfoil are already heavily affected by human activity (anthropogenic), it’s hard to clearly distinguish the plant’s specific impact from that of other anthropogenic sources.

That said, when Eurasian milfoil settles into a lake, plant diversity suffers (even when less than 50% of the bottom surface has been invaded).

Various theories have been put forward on how these plants might harm vertebrates and invertebrates alike. For instance, when Eurasian water-milfoil spreads, the amount of dissolved oxygen in the water can drop, possibly asphyxiating other species. Still, validating or invalidating these theories requires further research.

As for economic impacts, thick mats of these plants can not only decrease the esthetic appeal of beachfront properties, but also prevent recreational activities like swimming, boating and angling fishing there, ultimately affecting the properties’ monetary value. 

Help stem the spread of Eurasian water milfoil

  1. Prevention
    1. Always clean your boat and other watercraft.
    2. Don’t navigate in areas invaded by Eurasian water milfoil.
  2. Eliminating milfoil, including pulling it out by hand
    You can try to eliminate milfoil various ways, but none of them is 100% effective, making simple prevention the most recommended approach. For example, cleaning watercraft reduces the risk of transporting this invasive plant to other bodies of water. Also, by avoiding areas infested by water milfoil, you prevent fragmentation, which is one of the ways the plant spreads and reproduces.
    Beyond prevention, you can pull the plant out by hand. It’s a long, complicated process, but it’s produced positive results in studies. If you do try it, remember to remove not only the stems, but also the root system—and to dispose of the plants on dry land.  

The following techniques are also used, but they require ministry approval and often the guidance of specialists:

  • Covering with tarps
  • Freezing 
  • Herbicides
  • Biological

Non-recommended approach (based on tests):

Cutting or raking: Tests have shown raking and cutting to be ineffective, largely because milfoil can rapidly reproduce from the fragments left behind. When trying to stem the spread of this invasive plant, we need to remember that it can reproduce in two ways: sexually and by stem fragmentation). As a result, fragments created by boat traffic and by cutting or raking allow the plant to re-establish itself at the bottom and invade new areas of the lake or pond.

Rusty crayfish (Orconectes rusticus)

Anglers used to rely heavily on rusty crayfish as live bait until the Québec government banned the practice. The species still managed to spread quickly, and it now inhabits the Blanche River watershed and other bodies of water in the province.

How to identify rusty crayfish?

  • Colour: The shell ranges between greyish-blue and greenish brown, with almost always a red spot on each side. Black stripes are often observed at the end of each claw or pincer.
  • Length: Adults can reach 11 cm long.

Ecological and environmental impact

The introduction of rusty crayfish can create an imbalance in aquatic ecosystems. They compete with native crayfish, ultimately eliminating them from the invasion site. Rusty crayfish also deplete food sources by feeding on snails, clams, leeches, aquatic insects and fish eggs. And this drop in resources can harm fish populations.  

Help stem the spread of rusty crayfish

  • Inspect and clean your watercraft.  
  • Never release into the water fish or aquatic species that come from another body of water.

Zebra mussel (Dreussena polymorpha)

Zebra mussels are small bivalve, fresh-water mollusks. Though none have been spotted in or around Val-des-Monts, they’ve made their way into both the St. Laurence and Ottawa rivers nearby. That’s why we need to take precautions to avoid introducing zebra mussels into our lakes. 

How to identify zebra mussels?

  • Length: 0.5 to 5 cm.
  • Colour: brownish shell often covered in beige zigzagging stripes.

Economic and environmental impact

The zebra mussel is a formidable invader with a hefty environmental and economic impact.

Because it readily attaches itself to a wide variety of underwater surfaces, it can, for instance, clog drinking-water intakes, aquatic equipment and most other submerged infrastructure. Fixing these issues is both difficult and costly.

What’s more, the zebra mussel hinders biodiversity, causing native fresh-water mussels to disappear and harming fresh-water fish species, for example. The invader also filters water, increasing its transparency and, as a result, creating ideal conditions for aquatic plants to proliferate in. This greatly affects the ecosystems it invades.

Finally, zebra mussels reproduce alarmingly fast, with females able to lay between 30,000 and 1,000,000 eggs every year. The hatched larvae, which are invisible to the naked eye, can spread over long distances thanks to the current—and the water needs to be only 12 degrees Celsius or higher for propagation to occur.

Help stem the spread of zebra mussels

  • Always inspect and dry your watercraft and other aquatic equipment.  
  • Discard any foreign organisms and substances outside of the body of water you’re on, to prevent them from invading a natural setting. 

To date, efforts to eradicate invasive species from bodies of water have failed, hence the critical importance of being proactive and preventing their introduction at the outset.

Tics and mosquitoes

In Québec, a mosquito bite can infect you with viruses like the West Nile strain and those of the California viral serogroup. The mosquitoes carrying these diseases inhabit both urban and rural areas, including forests and woodlots, and can transmit the viruses at different times of the day.

That’s why it’s important to protect yourself from such bites when you venture outdoors whenever these insects are active. And if you travel outside of Québec, be sure to inquire about the presence of mosquitoes and when they’re most active.  

How to protect yourself against the danger of mosquito bites

Not surprisingly, the best protection against the diseases spread by mosquito bites is to avoid getting bitten in the first place. So consider these measures to reduce the risk:

  • Wear long, light-coloured clothing when you go outside, especially when mosquitoes are active.
  • Use mosquito repellent. 
  • Be sure to have secure screens on house doors and windows, and on your tent and camping shelter.
  • Cover baby strollers and cribs with protective screens when you’re outdoors.
  • Find ways to reduce mosquito populations in your surroundings.  

How to protect yourself from tick bites

Tick bites can also transmit diseases to humans, most notably Lyme disease. The best protection? Avoid tick bites in the first place.

To avoid getting bitten when you’re out in the forest, a woodlot or tall grass, be sure to do the following:

  • Wear long sleeves and pants, and cover yourself as much as possible.
  • Use a Deet-based or icaridin-based insect repellent.
  • Stay in designated walking paths or trails.
  • Keep vegetation in check around your house, especially near high-traffic and children’s play areas.
  • To learn more about preventing tick bites and reducing tick populations in your surroundings, consult the Protection and prevention section of the Québec government’s website.

Removing a tick after a bite

If you’re bitten, remove the tick as soon as possible. To remove a tick from your skin, use a tick remover (follow the manufacturer’s instructions carefully) or tweezers. Avoid using your fingers or fingernails.

Steps for removing a tick

  1. Grasp the tick with tweezers as close as possible to your skin, but don’t press on the insect’s abdomen, because that increases the risk of transmitting the bacteria responsible for Lyme disease.
  2. Pull the tick gently, but firmly and continuously, without turning it or crushing it, so you remove it entirely without “breaking” it. If the tick’s head stays implanted in the skin, try to remove it delicately with tweezers; if you can’t, leave it in place and let the skin heal. 
  3. Because the tick can be useful if you need to see a doctor, place it in a container that closes tightly, such as one used for pills. On the container, write the body that was bitten and the date the tick was removed. Then, store it in the refrigerator.
  4. After removing the tick, clean your skin with soap and water, and wash your hands thoroughly.

What to do after you remove the tick

  1. Write down the date and location you were at when bitten. Also note what part of your body was bitten. This information could be useful if you consult a health professional.
  2. If you have Lyme disease symptoms in the days, weeks or months after the bite, contact Info-Santé 811 or consult a doctor, and share the details of the bite as you noted them. If you visit a doctor, bring the tick with you in a closed container (see Steps for removing a tick), as the doctor may decide to have it tested so the information can then serve to track the spread of blacklegged ticks.
  3. What to do if you’ve been bitten by a tick in Québec’s Estrie, Montérégie, Outaouais, Mauricie-et-Centre-du-Québec regions or elsewhere in Canada or the United States:
    • Once you’ve removed the tick, call Info-Santé at 811. The medical staff will advise you on seeing a health professional or not. Also, the assessment may result in your being prescribed a preventive antibiotic.
    • Again, if you see a health professional in person, bring the tick with you.

Removing a tick from an animal and recommendations for after

Here’s a link to English-language tips on removing a tick from your pets. You’ll also find French-language information and recommendations on removing ticks from pets on the ministère de l’Agriculture, des Pêcheries et de l’Alimentation website.

And for more insights on warding off ticks and mosquitoes, visit the advice and protection section of the Québec government’s website.

Important note: Please don’t assume that the above list of invasive species is complete. Other invaders might already be in Val-des-Monts or might be able to move into the area.


First, no matter what type of recreational activity you enjoy, you can help slow and even stop the spread of invasive species. Second, invasive species go beyond plants and vegetation: they can also be animals and insects, both vertebrates and invertebrates.

Camping: Don’t transport firewood. Buy it locally and leave whatever might be left over where you got it.

Boating: Wash your boat or watercraft before transferring it to another body of water. Here’s a short video on the simple boat cleaning process involved.

Hiking: Before leaving the area in which you hiked, remove the mud, plants and seeds that may have stuck to your shoes, boots or other gear.

Aquarium lovers: Don’t throw aquarium water into a local body of water, your toilets or your water garden. Use it instead to water a plant bed or to moisten your composting.

Travel: Don’t bring plants, parts of plants, seeds or fruits to or from your travel destination.

Shoreline living: Keep your shoreline intact and well vegetated so that it can filter and absorb nutrients that might otherwise promote the growth of invasive aquatic plants.