Canada waterweed, Elodea canadensis, is a member of the Hydrocharitaceae family.
Canada waterweed was first detected in PEI at Knox’s Damn, Head of Montague, in 2005. It has since been detected in Pondside Park, Stratford.
The plant has been commonly used as an aquarium plant, and may have been introduced to PEI during an aquarium dump.
Here are some key features that may help to positively identify Canada waterweed:
Leaves are oblong, green, translucent, and in whorls of 3 (occasionally 4) around the stem
Leaves are 6-15mm long, 1-5mm wide and the leaf tips taper to a blunt point
Canada waterweed is dioecious – male and female flowers occur on separate plants.
Flowers are often not produced.
From June to August, small white flowers occur on the ends of thread-like stalks, floating at the water surface.
Fruit capsules, if produced, are 6mm long and ripen underwater.
Reproduces mainly by stem fragments (stolons) and overwintering buds (short compact branches that appear in late summer)
Stems are branched, round and slender, and can be 1 to several metres in length
Flowers are white-pale purple and occur at the end of the stem, usually at or just below the water surface from June- August
Depending on growing conditions, it can vary in appearance from being robust, bushy plants to spindly plants with very few leaves
They produce adventitious roots which can hang free in the water or root at the water bottom.
What it does in the ecosystem
Canada waterweed is an underwater perennial that can be a major problem in slow-flowing watercourses.
Canada waterweed spreads rapidly and easily outcompetes native species for space in aquatic ecosystems.
It reproduces by seed and by budding (regeneration of a new plant from an outgrowth of the parent plant), but its most prolific method of reproduction is fragmentation. Even tiny pieces of the plant that float to a new location will re-establish and create another outbreak site.
Over time, stolons (horizontal stems) will spread across the bottom of the waterbody, forming a dense bed. These beds can change local water movement, trap sediment, reduce light intensity, and create anoxic conditions.
These effects combine to threaten overall ecosystem health, reduce biodiversity, and decrease the economic and recreational value of an area.
Canada waterweed infestations can disrupt human recreational activities such as fishing, boating, canoeing, and swimming.
The build-up of plant material over long periods of time can affect the irrigation of crops and drainage by clogging infrastructure like pipes and ditches.
Canada waterweed outbreaks have also caused reduced water flow to hydroelectric power plants and negatively impacted catch weights for commercial fisherman. This plant is not only a concern for the local ecosystem but has significant socioeconomic impacts as well.
The best way to manage a plant infestation is to prevent it from happening in the first place.
It is key to clean, drain, and dry all aquatic equipment when moving to another location, especially if you have been near a Canada waterweed infestation.
Don’t let it loose! Never empty aquarium waste into a natural area. This practice has facilitated the spread of Canada waterweed and other invasive species including goldfish and red-eared slider turtles.
When managing invasive plants in an aquatic setting, you must first obtain a Watercourse, Wetland and Buffer Zone Activity Permit from the PEI Department of Environment, Energy, and Climate Action.
It is best to apply at least six weeks before your planned work start date.
Before selecting a control method, consider the following:
The size of the infestation.
The amount of effort you are able and/or willing to expend.
Often, multiple control methods are used simultaneously.
Ensure you also consider the local ecosystem and what other organisms or ecological processes may be affected by management.
Place a filter at any downstream outlets of the watercourse or wetland to prevent dispersal by fragmentation. The filter will catch fragments of the plant that escape controls and float away.
Always begin work at the upstream end of an infestation. Plants that move in from an upstream location
Planting densely along the banks of affected watercourse can reduce light availability for Canada waterweed, reducing its fitness.
There are many ways to tackle an infestation of Canada waterweed, all of which are fairly involved and labour-intensive.
If it is possible to control the water level, draw-down control (draining) may be used. During draining, it is important to prevent all fragments of Canada waterweed from moving away with the water, as these will create new infestations.
Cutting is a possibile method of control and is best undertaken before July when the plant growth is at its peak.
There are many ways to cut and remove the plant, including rakes, chains, knives, and more specialized equipment.
In the past, snails and aquatic herbivores have been used as a biological control method. However, this involves introducing yet another exotic species into the ecosystem and is therefore not recommended.
Chemical control is never to be used when managing Canada waterweed on PEI, as herbicide use is unlawful in or nearby an aquatic environment in the province.
Ultimately, how you choose to manage an outbreak of Canada waterweed should be first and foremost considerate of the other members of the ecosystem. While planning, always keep in mind how to best restore the area to its natural state and preserve local biodiversity.
CLEANUP AND REMEDIATION
As Canada waterweed reproduces by fragmentation, it is crucial that all invasive plant parts be collected and disposed of properly to prevent any further spread.
Disposal can vary based on the site, the amount of plant material, and your equipment limitations.
If there is a dry area away from foot or wildlife traffic, plants can be piled a left on site to decompose. Plants must be piled in a way that will not allow them to reenter any watercourse, as this will result in further spread.
If no suitable area is available to pile the plant material, material must be secured in clear plastic bags, marked “invasive plant” or “Canada waterweed” and disposed of in regular waste collection (BLACK bin). Up to two additional bags can be placed beside the cart.
For loads larger than what would fit in a ½ ton truck, reach out to the PEIISC for specific disposal instructions.
Clean all equipment and clothing ensuring all plant parts have been removed before moving on to prevent inadvertent spread.
Repeated management over several years may be necessary depending on the effectiveness of initial management tactics.