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Eurasian watermilfoil: one of Michigan’s biggest invasive threats

Michigan Tech Research Institute ecologist Kevyn Juneau speaks about one of Michigan’s most invasive aquatic plants, Eurasian watermilfoil, for the #MIspecies campaign. You may or may not know the name, but you’ve definitely seen the impact. Let’s learn about one of the most invasive and damaging aquatic plants in Michigan.

Adrian de Novato: What exactly is Eurasian watermilfoil?

Eurasian Watermilfoil
Eurasian watermilfoil

Kevyn Juneau: Eurasian watermilfoil (EWM) is an aquatic plant that has become quite prolific in freshwater systems throughout the world. In fact, it’s been documented on every continent except for Antarctica. In the United States, it is present in every state except for Hawaii. It has been in lower Michigan since the 1960s. EWM can be distinguished from other aquatic plants by its characteristic feather-like leaves. There are four leaves that originate from each node. Nodes are the location where leaves attach to the stem. The leaves have a single main axis, which can grow up to about 4 cm, that has 12-24 threadlike leaflets coming off it. EWM is a submerged plant except for its pink flowers that grows a few inches above the water’s surface in mid to late summer. EWM can grow fast and extremely dense. There have been reports of animals walking on top of EWM mats. Because of its tendency to grow early and fast, it has become a major nuisance in many of the waterbodies in which it is present.

Adrian de Novato: What are the ecological and economic dangers of allowing Eurasian watermilfoil to grow? We call it an invasive species, but why?

Kevyn Juneau: By definition of U.S. Executive Order 13112: FR Doc. 99–3184, invasive species are “those with prevalent populations outside their native habitats with economic and ecological ramifications.” EWM has its share of both. EWM is considered one of the most significant aquatic invasive species in the U.S. Aquatic invasive species cost billions of dollars every year in damage, losses, and management; control for EWM alone is upwards of $400 million a year in the country. According to the U.S. Government Accountability Office, Michigan has spent millions of dollars to control aquatic invasive species, which includes EWM. The reason so much is spent on controlling this plant is because of its impacts on the economy and environment. EWM can grow in a wide range of conditions allowing it to readily invade all sorts of lakes, ponds, and streams. It has roots, so even if the water column has low nutrient contents, like that of Lake Superior, it is able to obtain nutrients vital for its growth from the sediment. Once present, EWM has been shown to lower the value of lake-front property approximately 10% in the Great Lakes region and up to 19% in the Pacific Northwest. Because of its dense growth, EWM can also inhibit commercial and recreational boat traffic, foul fishing gear, and impede recreational activity, thus leading to a reduction in local economies.

EWM wrapped around boat motor.
EWM wrapped around boat motor.

Ecologically, dense populations of EWM can shade out native species and reduce species diversity. It does so by growing in the spring much earlier and faster than native species. In Torch Bay, Portage Lake in the Keweenaw Peninsula, for example, EWM begins to grow when there is ice still present on the lake! Dense populations also restrict water flow and mixing of water resulting in lower dissolved oxygen. Decomposition of the large amount of EWM biomass in the fall can lead to further reductions in dissolved oxygen concentrations necessary for aquatic animals. EWM also disrupts food webs, potentially leading to lower fish production.

A major concern is that EWM has the ability to hybridize with the native northern watermilfoil. This gives it the potential to grow more vigorously in areas ideal for northern watermilfoil and can further expand its range northward into colder waterbodies where it wasn’t present in the past but northern watermilfoil was. The hybrids are also proving to be more tolerant to herbicides.

Adrian de Novato: The name seems like it might be something of a hint, but where did it come from? Do we know how it was introduced into the Great Lakes?

Kevyn Juneau: EWM is native to Eurasia, but can now be found throughout the world. It may have been introduced into Chesapeake Bay via ship ballast in the late 1800s, but it’s also been suggested that it may have escaped cultivation much later than that. The earliest confirmed detection is from Belch Spring Pond in Washington, D.C. when it was found in 1942. It was accidently and intentionally spread across the country ever since. It was initially spread due to the ornamental plant trade, as escapees of cultivation, and was dispersed by boats and waterfowl. EWM was at one time used as packing material for worms sold to anglers. EWM was also planted to “improve” fish habitat in the 1950s. It’s unknown how it was first introduced to the Great Lakes, but it was most likely introduced accidently as a fragment. The first report of EWM in the Great Lakes region was 1949 when it was found in Put-in-Bay, Ohio on Lake Erie. The first report of it in Michigan comes from a herbarium specimen collected in St. Clair County in 1961. It made its way to the Upper Peninsula in the early 1970s when it was found in Little Bay de Noc, Escanaba. It wasn’t until 2006 that it was discovered in the Les Cheneaux Islands in northern Lake Huron. It was first reported in Pike Bay, Portage Lake in the Keweenaw Peninsula in 2012.

Adrian de Novato: How are you involved in combatting this invasive plant?

Kevyn Juneau: I am involved in a project with Michigan Technological University, the Michigan Tech Research Institute, and other partners throughout the Upper Peninsula to better understand the ecology of EWM so we can develop a more holistic, integrated pest management approach for controlling it. For the past few years we have been examining the efficacy of strategic herbicide applications, Diver Assisted Suction Harvesting (DASH), benthic barriers, and biological controls to manage EWM and its hybrids throughout Michigan. We also developed a website that has information about our project, EWM biology, control, mapping tools, and links to management plans used throughout the Great Lake States.

Adrian de Novato: How can people help?

Kevyn Juneau: First and foremost, we must properly identify EWM and its hybrids and leave its control to the trained experts—those with the appropriate pesticide certifications. There is an epidemic of improper pesticide use in our aquatic systems because landowners can easily misidentify important native species as EWM and illegally take it upon themselves to treat near-shore areas and around docks. Native species are necessary to maintain healthy aquatic systems and the vigorous fisheries the Great Lakes states are known for, so it’s vital that we do not eradicate them. Not only does improper pesticide use also lead to increased pollution in our waterways, but much like how misuse of antibiotics can lead to drug resistant bacteria, pesticide misuse leads to pesticide resistance rendering herbicides ineffective at killing the invasive plant.

Secondly, we must halt the spread of EWM and its hybrids. EWM is able to reproduce asexually by fragmentation so the most effective way to do halts its spread is to clean, drain, and dry any equipment (boats, trailers, fishing gear, water skis, etc.) when going from one waterbody to another. Fragments as small as 10 cm can remain viable and lead to new populations; therefore, it’s important to be vigilant and persistent when cleaning equipment.

It is inevitable that this species will spread, so we rely on early detection and rapid response to eradicate new infestations before they overtake waterbodies. If EWM is suspected to be present, it should be reported immediately to the DNR, the local conservation district, or the cooperative invasive species management area coordinator.

For more information on EWM and our project visit our webpage:

The #MIspecies campaign

Help us raise awareness about the serious economic and environmental issues as a result of aquatic invasive species and learn more about how you can help make a difference in your local community at

About Kevyn Juneau

Juneau is a Certified Associate Ecologist and an assistant professor of conservation and environmental science at the University of Wisconsin-River Falls where he studies invasive plant ecology in order to develop environmentally sound integrated pest management (IPM) practices. IPM aims to reduce the risks of pests and pesticides on human and the environment.

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