Understanding Eurasian Watermilfoil: What is it, How Did it Get Here, What are its Impacts, and What Can We Do to Prevent its Spread?
What is Eurasian Watermilfoil?
Eurasian Watermilfoil is an alien of sorts…but not the kind of alien that you may be thinking of! It is called an alien, or invasive species, because it is not native to North America, but rather Eurasia – hence the name Eurasian Watermilfoil. This aquatic plant has a “feathery” appearance and usually grows between 6 – 9 feet tall under the water but can reach heights of up to 20 feet. That’s taller than a one-storey house! In addition to being very tall, this rooted, slender plant is also a fast-growing perennial, meaning it regrows every year and is persistent through all seasons due to root crowns that are preserved throughout the winter.
Eurasian Watermilfoil tends to take over parts of the lake where it establishes, growing in thick, dense mats in shallow waters (typically between 1-4 m deep but sometimes as deep as 10 m) with branches that reach the top of the water and form a canopy. In the summer, you can spot this invasive species without even going in the water by observing its orangey-red flowers poking through the surface of ponds and lakes in late July and August. But be careful! Eurasian Watermilfoil also has a very close look-alike which is native to Ontario, called the Northern Watermilfoil. These two species can be distinguished from each other using the general rules depicted in this diagram:
How Did Eurasian Watermilfoil Get Here and How Does it Spread?
Now that we know what it looks like and how to differentiate it from native species, let’s learn a bit about the history of how it got here. As we mentioned previously, Eurasian Watermilfoil is originally from Eurasia (Europe and Asia), as well as northern Africa. It was introduced into Canada in the 1960’s and was first reported in Lake Erie in 1961. There are conflicting theories on how it got here but the two main speculations are that it arrived either through contaminated shipping ballast or through aquarium releases. Others also say it may have been introduced as fresh packing material for worms or even intentionally by anglers to improve fish habitat in lakes!
Regardless of its origins, Eurasian Watermilfoil is here and continues to spread further across Ontario to inland lakes via boats, boat trailers and equipment carrying plant fragments from infected waters. In fact, there are three main ways in which Eurasian Watermilfoil disperses: stem fragmentation, seed dispersal and stolon formation. Stem fragmentation occurs when stems either break off naturally from the plant after flowering, or from mechanical disruption from boat motors and propellers. The fragments then get dispersed via a combination of natural currents and recreational boating practices. It is important to note that Eurasian Watermilfoil is highly susceptible to mechanical disruption from boat motors and can spread extremely well when this happens. In either case, the plant is able to travel far distances to establish in a new area. It can also spread to new areas via seed dispersal, although this method is not as significant. Once established in a new area, the plant expands locally by using stolon formation where a stem grows along the ground from a parent plant to form new roots and vertical stems a few centimeters away. It grows best in waters with temperatures above 15°C, with high nutrients and little vegetation cover. However, these are only optimal conditions – Eurasian Watermilfoil is highly adaptable and can grow in a range of environments, allowing it to proliferate in virtually all waters in central and southern Ontario.
What are the Impacts of Eurasian Watermilfoil?
By now, you are probably thinking, “So what? What’s wrong with having this non-native plant in our waters?”. Well, Eurasian Watermilfoil is not just scary to swim in and frustrating to boat in (being tangled in a thick dense mat of “seaweed” is not fun), but it also interferes with fisheries, water quality and resident wildlife. It takes over native fish habitat by obstructing space and disrupting fish feeding patterns. You would not be able to cast a line in this mess without getting snagged – that’s if there were even fish there to catch in the first place! Not only does it invade habitat, it also can reduce oxygen levels in the water, therefore making the ecosystem less inhabitable for other aquatic species, including tiny invertebrates. Even worse, this plant can encourage the infestation of mosquitoes by creating stagnant water, and lower property values.
What Can We Do to Prevent the Spread of Eurasian Watermilfoil?
There are many simple measures that you can take in your everyday life to help prevent the spread of Eurasian Watermilfoil. These include the following:
- Avoid boating near areas or in lakes that are infested with Eurasian Watermilfoil since propellers can break fragments and spread them to other areas (check https://www.eddmaps.org/Ontario/distribution/viewmap.cfm?sub=3055 to see if Eurasian Watermilfoil or other invasive species have been found in your lake)
- Inspect and spray down your boat, trailer and fishing gear to get rid of plants and dirt before leaving each fishing spot
- Drain any water from your boat and gear (ballast tanks, bait containers, motor, drain bilge, livewell and baitwell) before leaving each fishing spot
- Dispose of unused bait in the trash
- Do not plant Eurasian Watermilfoil in your aquarium or backyard pond and avoid releasing aquarium contents into water bodies (instead put them in the garbage or return or donate unwanted plants and pets)
- Report Eurasian Watermilfoil and other invasive species to EDDMapS Ontario (https://www.eddmaps.org/), a web-based mapping system
Perhaps the most important thing you can do to prevent the spread of invasive species is to learn how to identify them and differentiate them from native species. With the help of this blog and other resources (refer to the “Sources” section at the end of this blog), you can learn how to spot Eurasian Watermilfoil, report it to invasive species tracking platforms, and avoid its accidental spread. To learn more about other invasive species in Ontario, visit http://www.invadingspecies.com/invaders/.
By Angela Vander Eyken
Cunningham, J. (2014). Invasive Species of the Pacific Northwest: Eurasian Watermilfoil Myiophyllum spicatum. https://depts.washington.edu/oldenlab/wordpress/wp-content/uploads/2015/09/Myriophyllum_spicatum_Cunningham_2014.pdf
Government of Ontario. (2018). Eurasian water milfoil. https://www.ontario.ca/page/eurasian-water-milfoil
Jensen, D. (2016). Eurasian Watermilfoil (Myriophyllum spicatum). Minnesota Sea Grant. http://seagrant.umn.edu/ais/watermilfoil
Lui, K., Butler, M., Allen, M., Snyder, E., da Silva, J., Brownson, B., & Ecclestone. (2010). Field Guide to Aquatic Invasive Species: Identification, collection and reporting of aquatic invasive species in Ontario waters (3rd Edition). Ontario Ministry of Natural Resources. http://www.invadingspecies.com/download/field-guide-to-aquatic-invasive-species-3rd-edition/
Menninger, H. (2011). A review of the science and management of Eurasian watermilfoil: recommendations for future action in New York State. Finger Lakes PRISM (Partnership for Regional Invasive Species Management). http://fingerlakesinvasives.org/wp-content/uploads/2014/03/NYISRI-EWM-Report_Final_11Nov2011.pdf
University of Minnesota. (2008). Identification of Eurasian Watermilfoil (Myriophyllum spicatum). https://www.lakesuperiorstreams.org/understanding/media/ewm_factsheet2008.pdf
Williams, H., Willmott, T., Wright, I., & Elliot, T. (2018). Eurasian water-milfoil management plan for Shawnigan Lake, BC. Cowichan Valley Regional District. https://www.cvrd.bc.ca/DocumentCenter/View/89788/Shawnigan-Milfoil-Report_Final