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Wetlands - Invasive Species

Whether they are called invasive, nonnative alien, exotic, or nonindigenous, introduced species are those that evolved elsewhere and have been purposely or accidentally relocated . While some species have invaded habitats on their own (e.g., migrating wildlife, plants and animals rafting on floating debris), human exploration and colonization have dramatically increased the diversity and scale of invasions by exotic species. Introduced species often find no natural enemies in their new habitat and therefore spread easily and quickly.

There are a wide range of wetland invaders. Some of the more problematic species in CLOCA’s jurisdiction are listed below.

Purple Loosestrife

European Frog-bit

Common Reed

Eurasian Watermilfoil

Flowering Rush

Water Hyacinth

Yellow Iris

Potential Threats

Japanese Knotweed

 Himalayan Balsam



Purple Loosestrife (Lythrum salicaria)
Purple Loosestrife
Purple Loosestrife
  • Native to Europe
  • Brought to North America by settlers in the early 1800’s
  • Used extensively in flower gardens
  • Mature plants can produce in excess of 2 million seeds annually
  • Competes with and displaces native wetland vegetation
  • Seeds are hardy and can remain dormant in the seed bank for many years
  • Biological control is available for large infestations
  • Mechanical control is successful by removing entire plant during flowering before seed set

    Distribution Map (PDF - 500kb)

Biocontrol was implemented in Cranberry Marsh with the release of 5000 Galerucella beetles in 1999, to learn more on the release see Cranberry Marsh Restoration Purple Loosestrife control.

European frog-bit (Hydrocharis morsus-ranae)
  • Originally from Europe and Asia
  • Introduced to the Ottawa Region in 1938 as a horticultural species
  • Looks similar to American frog-bit (Limnobium spongia)
  • Forms dense mats on the surface of open water thereby reducing native biodiversity
  • Reproduces both sexually and asexually, the latter being more dominant
  • Few methods of control, removal by hand is a temporary solution
  • Plants are spread to new waterbodies through boat propellers and other aquatic equipment
  • European frog-bit is commonly sold as a water garden plant

    European frog-bit Fact Sheet
European frog-bit
Source: European frog-bit, http://www.qc.ec.gc.ca/csl/inf/inf036_e.html, Richard Carignan Universit?de Montréal, (2005)

Common reed (Phragmites australis)
Common Reed
Source: Common Reed, Caroline Savage, St. Lawrence Centre

Flowering rush (Butomus umbellatus)
  • Native to Eurasia, introduced in late 1800s as an ornamental plant
  • Flowers from July to September. Produces clusters of white and pink flowers. Can be difficult to identify when not flowering
  • Can grow up to 1 metre high and a depth of 3 metres
  • Typically invades shorelines, disturbed areas, road sides
  • Dominates marsh areas and displaces native vegetation

Flowering rush

Water Hyacinth (Eichhornia crassipes)
  • Native to South America, brought to US in 1884 as a garden ornamental
  • Has been called ‘the most damaging aquatic weed in the world’
  • Can grow very quickly and completely take over water bodies if left unchecked. Can double population in two weeks
  • Each stalk produces 6-15 pink flowers
  • Releases hundreds of seeds which can last for up to 30 years
  • Disperses by seeds, fragmentation, root systems
  • Commonly sold in garden centres and nurseries
  • Can survive in almost any water body, can tolerate wide range of environmental conditions and pollutants

Water hyacinth
Yellow iris (Iris pseudacorus)

Yellow iris
  • Native to Eurasia, introduced as an ornamental plant
  • Commonly sold in garden centres and nurseries
  • Grows quickly in water bodies, ditches. Very difficult to eradicate
  • Disperses by seeds and fragmentation
  • Can grow to be 1.5 metres high
Japanese knotweed (Fallopia japonica)
  • Native to Japan, brought to United States in 1870’s as an ornamental plant
  • Can grow 1-2 metres tall, forms dense patches
  • Found along stream banks, roadsides, disturbed areas
  • Seeds dispersed by wind, can spread through roots up to 15 metres long, can reproduce from fragments as small as 1cm

Japanese Knotweed

Himalayan balsam (Impatiens glandulifera)

Himalayan Balsam

  • Native to India, brought to Canada in early 1900’s as a garden ornamental
  • Rapid growth, can reach heights of 3 metres and quickly outcompetes native plants
  • Thrives in moist areas, especially stream banks and shorelines
  • Seeds dispersed by water



Potential Threats

There are several non-native species which are not yet found in CLOCA jurisdiction. It is everyone’s responsibility to help prevent these species from entering our lakes and streams.

  • Floating Heart (Nymphoides peltata)
  • Fanwort (Butomus umbellatus)
  • True Watercress (Rorippa nasturtium-aquaticum)
  •  Water Solider (Stratiotes aloides)
  • Water Chestnut (Trapa natans)

Additional Links

For additional information on invasive species see Forests and Streams sections.


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