Aquatic Invasive Species in Ontario

This week is designated as Rivers to Oceans Week. As such, we decided to write this article, focusing on one of the biggest challenges in Ontario’s aquatic ecosystems – invasive species.


Alien Species: Organisms found in an area outside of their normal geographic range.

Invasive Species: An alien species whose introduction does or is likely to cause disruptions in the new ecosystem or to human health.

Invasive Alien Species: Species that are transported to a new environment and are able to rapidly multiply, out-compete native species, and change native habitats.

Geographic Range: The geographical area within which a particular species can be found.

Native Species: Species that are indigenous to a given region or ecosystem if their presence in that region is the result of only natural processes, with no human intervention.

Watershed: It’s a land area that channels rainfall and snowmelt to creeks, streams, and rivers, and eventually to outflow points such as reservoirs, bays, and the ocean.


Across the planet, there are countless animal, plant and even micro-organism species that have moved beyond their natural geographic ranges and habitats – only to become established in completely new locations. Sometimes species that are traditionally found in one part of Canada will become established outside of their usual range, in places where they have not historically been found. However, most come from outside of Canada and were relocated here due to human activities – often hitching rides into the country from imports such as fruit crates, or on the bottom of ships. Those species that become established in areas outside of their usual range are known as alien species, while those alien species that are capable of causing significant harm to our environment, economy, or people are referred to as invasive alien species.

In Canada, invasive species are amongst the greatest threats to the survival of our diverse wildlife. When these species arrive (often accidentally) from elsewhere in the world, and their new ecosystem is absent of natural predators, they tend to kill, crowd out, or otherwise devastate native species and their ecosystems. These invasive plants and animals not only threaten to transform the wildlife, woodlands, and waterways that Canada’s people and wildlife rely upon, but also cost the country billions of dollars in losses to forestry, agriculture, fisheries, and other impacted industries.

Invasives in Ontario

The province of Ontario has the greatest number of invasive species both on land and within its waterways. The province holds the highest number of invasive plant species in the country with 440 identified and also holds the most non-native fish species (26 unknown) – which is twice the amount in Quebec, Alberta, and Manitoba. As well, within the Great Lakes, 180 non-native and invasive species have been found. A few of the reasons why Ontario is a high-risk province for invasive species include:

The Invasive Species Centre

The Invasive Species Centre was incorporated as a non-profit in 2011, establishing a hub for collaboration and knowledge-sharing. The Centre works to prevent the introduction and spread of high-risk invasive species in Canada by connecting stakeholders with the necessary knowledge and technology.

The Invasive Species Centre established best management practices database in which they provide a collection of easily accessible resources on various invasive species in Canada. The database includes best management practices, response plans, management plans, action plans, and protocols to help individuals and organizations manage terrestrial and aquatic invasive species. The management documents and recommendations vary across jurisdictions to address different objectives and criteria. It is important to check with local rules, regulations and authorities before implementing any management strategies.

Lake Simcoe

Some areas, such as the Lake Simcoe watershed, are considered invasive hotspots, with a wide number of invasive species being found there. These species are one of the greatest threats to Ontario’s waters.

Figures 1, 2 &3 – Spiny Water Flea, Purple Loosestrife, Zebra Mussels

A variety of aquatic invasive species have been found in the Lake Simcoe watershed, such as the zebra mussel, round goby, spiny water flea, purple loosestrife, and Eurasian watermilfoil. Many of these species found in Lake Simcoe have spread over time through the Great Lakes from activities such as boating and angling.

Figures 4 &5 – Giant Hogweed, Garlic Mustard

Not only does Lake Simcoe hold a number of aquatic invasive species, but you can also find a number of terrestrial invasives as well. Terrestrial invasive species include giant hogweed, garlic mustard, and others that are introduced through ornamental gardening or through the practice of importing seeds in the soil, or the treads of boots and/or tires.

Most of the aquatic and terrestrial species within the Lake Simcoe ecosystem are unintentional new introductions. Aquatic species can arrive in the Lake Simcoe watershed attached to boats, boat trailers, fishing gear, or from individuals emptying the contents of aquariums into natural waterways. The spread of invasive species causes a reduction in the abundance of native species, is the main contributor to species becoming at risk of extinction and disrupts nutrient and energy cycles. These species can also have a significant impact on the region’s economy, due to loss of revenue relating to natural resources or increased costs for monitoring, species removal, or facility maintenance.

Invasive Species Control

Once established, invasive species can be incredibly difficult and costly to remove. When prevention efforts fail, early detection is extremely vital, so that the necessary steps can be taken to fully comprehend their impact, eradicate or contain the species, or mitigate their impacts.

Local watershed monitoring programs are in place and are there to record early detection when it comes to aquatic invasive species. Monitoring programs, including fish diseases, exist in adjacent watersheds to Lake Simcoe, and in the Great Lakes as well. However, terrestrial monitoring is more limited. As a consequence, less is known about them and their impact on the Lake Simcoe watershed.

Figure 6 – Invasive Species Management

The number of invasive species continues to expand, and this expansion is only expected to increase as climate change worsens. The introduction and spread of these species are expected to have a greater impact on Ontario, as the province makes up a significant portion of Canada’s population. The estimated annual cumulative loss of revenue for Canada caused by the impacts of only 16 invasive species spanning forests, fields, and waterways, is estimated to be between 13.3 to 34.5 billion dollars.

Policies and programs continue to emerge at local, provincial and federal levels to help manage the threat that is invasive species. Currently, the regulatory tools available for controlling high-risk human pathways are limited in their scope. To help with this, stakeholders and partner organizations are working together to focus on policies and programs for both terrestrial and aquatic species. For example, using public education, outreach and stewardship to prevent the introduction of new invasive species.

Economic Impact

Figure 7 – Economic Impact of Invasive Species

Throughout Canada, invasive species pose economic threats at every level. The economic costs of invasive species are much lower when funds are consistently invested in prevention and early detection efforts – as stated previously, once an invasive species spreads and takes hold – it is much more difficult and expensive to manage.

Direct Economic ImpactsIndirect Economic Impacts
Costs for management, research & monitoring programsLoss of ecosystem services
Reduced crop yield Reduced biodiversity & resource production
Job losses Impacts to tourism & recreation
Damage to infrastructure Reduced property values
Impacts to international trade & tariffs
Table 1 – Direct & Indirect Economic Impacts

2019 Economic Impacts Study

Between 2017 and 2019, the Invasive Species Centre reached out to Ontario municipalities and conservation authorities via phone and email to find out how much they spend on invasive species each year. They received data from 147 municipalities and 23 conservation authorities.

Figure 8 – Municipality expenditures

The report estimates how much Ontario’s municipalities and conservation authorities are spending on invasive species, but these numbers are only a fraction of the economic impacts created by invasive species. According to this study, the combined potential impacts on agriculture, fisheries, forestry, healthcare, tourism, and the recreation industry are estimated to amount to around $3.6 billion per year in Ontario. See figure 9 to see where this money goes.

Figure 9 – Expenditures for Individual Species

According to this data, the invasive species that municipalities and conservation authorities spend the most money on is the emerald ash borer, with the next highest expenditure for municipalities being zebra mussels and the gypsy moth. For the complete study, please see here.


There are so many vital components and details when it comes to invasive species – and particularly aquatic species. Almost too many details to discuss in a brief article. As such, this article included just a simple introduction to the topic. If you have an interest in learning more, see the links included throughout the document.

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