top of page
AliensAreInvadingArtboard 19in.png
A Guide to Restoring Biodiversity in the Upper Twelve Mile Creek Watershed

Twelve Mile Creek is being invaded by aliens, but not by the type you see in science fiction movies.

What are invasive species?
Invasive species are alien invaders that have spread outside of their natural range to areas like the Twelve Mile Creek, either on purpose or by accident. This puts our native fish, plants, animals, and their habitats at risk.
Why are they of concern?

Alien species that have spread to new environments often lack predators and other natural controls needed to maintain a healthy, balanced ecosystem. These invasive plants, insects and fish have the ability to quickly overtake an area. This can cause irreparable damage to important habitats and ecosystems. When invasives move in, the plants and animals that benefit us get crowded out. 

How can you help?

Support the health of the Upper Twelve Mile Creek with these simple steps


Identify alien species on your property or on your nature walks


Report sightings using the free EDDMapS app on your phone


Remove the alien species using the proper method


Replant the area with native species

Sign Up To Volunteer


Join us to replant targeted areas near Short Hills Park with beneficial native species to help restore the ecological balance of the creek. 

Choose from 9 dates this October. Events will run for approximately 3 hours at a location within 10 minutes of Short Hills Park.

Top 8 Plants

The most prominent invasive species found in the Upper Twelve Mile Creek
These are the top 8 most commonly reported invasive species in the Upper Twelve Mile Creek watershed. They are also included here because they can be removed without the use of herbicides. 
Asset 22top-8.png

English Ivy

Identify: Notice creeping, climbing vines with dark green leaves.

Remove: Cut the vines at the base of the plant and gently remove them from trees or structures.

Replant: Solomon’s Seal

More info

Asset 18top-8.png

Garlic Mustard

Identify: Look for heart-shaped leaves with toothed edges and a distinct garlic odor when crushed.

RemovePull out the entire plant, including the root, before it goes to seed.

ReplantWild Ginger

More info

Asset 16top-8.png

Purple Loosestrife

IdentifyNotice tall spikes of purple flowers and pointed leaves with a smooth texture.

Remove: Cut stems near the base before seed production and remove entire plant. 

Replant: Marsh Marigold or Swamp Milkweek

More info

Autumn Olive

Asset 23top-8.png

IdentifyLook for pointed leaves that are shiny on one side, and small yellow flowers or speckled red berries.

Remove: Cut the shrub at the base and remove roots to prevent reestablishment.

ReplantServiceberry or Spicebush

More info

Common Periwinkle

Asset 24top-8.png

Identify: Observe trailing stems with dark green glossy leaves and purple flowers.

Remove: Pull the plant from the ground, including root system, to prevent regrowth.

Replant: Wild Ginger or Wild Geranium

More info

Asset 21top-8.png

Black Adler

Identify: Look for trees or large shrubs with cone-like fruits and leathery leaves that have toothed-edges and an indented tip. 

Remove: Cut the tree close to the ground and remove the stump to prevent resprouting.

Replant: Red Osier Dogwood

More info

Buckthorn (common & european)

Asset 15top-8.png

IdentifyLook for dark bark, oval leaves with distinct veins, thorny twig tips, and black berries.

Remove: Cut the trunk close to the ground, and dig out the root system to eradicate the plant.

Replant: American Hazelnut

More info

Asset 17top-8.png

Multiflora Rose

Identify: Look for arching stems with curbed thorns and clusters of white or pink flowers.

Remove:  Cut the stems close to the ground, and dig out the root system to prevent regrowth. 

Replant: Red Oiser Dogwood or New Jersey Tea

More info

Other Alien Species


Asset 20top-8.png

Hundreds of Invasive pet goldfish and baitfish are dumped into Twelve Mile Creek or nearby ponds, storm sewers and streams each year. These aliens can grow to be the size of a football by out-competing with native fish for their natural habitats. 

If you can no longer care for your goldfish, consider donating it to a garden nursery, local school, or contact the place where you purchased the fish and ask if you can return it.

Asset 19top-8.png

Hemlock Wooly Adelgid

These tiny alien insects weaken and kill Eastern Hemlock trees, leading to less shade, weak streambanks, and water temperatures too high for native fish to survive. Look for tiny white masses at the base of hemlock needles. 

If you have confirmed that one or more of your hemlock trees is infested with HWA, consider treating them with a systemic insecticide. 

More Info

Help Us Locate Invading Aliens!




Download The App

Invasive species are invading our watershed, but if we don’t know where they are, it’s tough to stop their spread. Early detection of these aliens is essential to controlling their spread.

By reporting alien sightings, you will help create a living map of these invaders that will inform future removal projects. EDDMapS is a fast and easy way to map invasive species without any technical expertise. Simply download the app, take a picture with your device, note any important details, and submit! 



Invasive Species

Best Management Practices

  • Searchable species database: EDDMapS Species Information 

  • Identification guides: Quick Reference Guides - Ontario Invasive Plant Council 

  • Factsheets:

    • General: Digital Resources | Ontario's Invading Species Awareness Program   

    • *Highlight* Goldfish: Digital Resources – Invasive Fish | Ontario's Invading Species Awareness Program  

      • Don't Let it Loose!

    • Additional Misc. Fact Sheets & Postcards - Ontario Invasive Plant Council 

Native Plant Alternatives

  • Grow Me Instead - Ontario Invasive Plant Council 


  • Native Plant Suppliers for the Niagara Area, Ontario 

Other Resources

  • A Landowner's Guide to Managing and Controlling Invasive Plants in Ontario

  • Twelve Mile Creek Landowner Stewardship Guide 

  • Regional herbicide practitioners 

  • Link to EDDMapS with blurb from copy text 

  • Watershed map

bottom of page