On Sunday September 24th, the Great Lakes Water Walk will pass numerous yacht clubs and marinas that line Toronto’s waterfront. A “Stop Aquatic Hitchhikers” sign is a common sight where boats are docked. No, this sign doesn’t refer to swimmers who’ve gotten tired during a day at one of Toronto’s many beaches. These signs remind boaters to avoid accidentally spreading invasive species.



An invasive species is a plant or animal that is foreign to an ecosystem. Native elsewhere, they are introduced into a novel habitat where they are not a natural part of the food web. Invasive species reproduce rapidly and are not heavily predated in their new home. As a result, they spread quickly, degrade habitat, and outcompete native species for resources. For instance, aquatic invasive plant species commonly deplete oxygen in water, killing other plants and animals. Similarly, bivalves like zebra mussels consume all of the nutrients in water, leaving none for native species. Invasive fish species often prey on native fish larvae and eggs, negatively affecting native fish population growth. These habitat alterations often drive native species to extinction and can cause food webs to collapse.


Invasive species are usually introduced unintentionally. They can be carried unintentionally in the ballast water of cargo ships bringing goods to inland cities; they can settle on the side of recreational vessels that boaters trailer from lake to lake each summer; live bait for fishing can also become an established invasive species; some introductions have been traced back to released aquarium pets (ex. lionfish in the Atlantic Ocean). While only a very small proportion of non-native species that are introduced actually establish themselves and spread, the ones that are successful have a disproportionately negative impact on the habitat they colonize.


There are an estimated 180 invasive species that have established themselves in the Great Lakes, significantly changing the ecosystem. Maybe you’ve heard of round gobies, sea lampreys, alewives, purple loosestrife, or Eurasian milfoil? These invasive species negatively impact humans who rely on the Great Lakes for food, water, and recreation. Economically, an invasive species-driven ecosystem collapse damages aquaculture and tourism, including sport fishing. Invasive species can also harm humans: zebra mussels in the Great Lakes have notoriously sharp shells that can slice swimmers and boaters.


Controlling the spread of invasive species after their establishment is extremely difficult and expensive. So, government and environmental organizations dedicate their efforts towards preventing the introduction of new invasive species in the first place. By tracking invasive species that occur in the waterways connected to the Great Lakes, decision makers can take rapid action to prevent their introduction in the case of an emergency. They can also predict the economic impact an invasive species establishment would have on the Great Lakes’ industries, including fisheries, agriculture, and tourism. The most current example of prevention measures is in response to the spread of Asian Carp, an invasive species that has not spread through the Great Lakes, but is common in nearby and connecting waterways. Expert scientists work to forecast the spread of Asian Carp in order to establish physical barriers.


Education is a major tool against the spread of invasive species. If the general public is aware of the threat invasive species pose for the Great Lakes ecosystem, they can support monitoring programs by reporting sightings and ensuring they clean their recreational water vessels well before moving on to the next lake. The purpose of the Great Lakes Water Walk is to re-awaken our commitment to protecting the Great Lakes, and in so doing we need to be aware of the threats that impact the ecosystem. So spread the word, not the invasive species!

Join us on Sunday, September 24th 2017 for the Great Lakes Water Walk. More information is available at our website: www.greatlakeswaterwalk.ca.

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For more information on invasive species, check out these websites: