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Eurasian Water-Milfoil

The weeds...oh the weeeeeds!

Eurasian water-milfoil (EWM) is a non-native, invasive species to North America. EWM spreads primarily through fragmentation, meaning that if a homeowner rakes and fragments the plant or a boat propeller goes through a stand of EWM, each released fragment has the possibility of becoming its own fully rooted plant. This leads to the spread of the plant very quickly throughout local waterways.

Flowering spikes emerge above the water line once the plant has reached the surface, typically June to July. Fruits develop later in July or August and continue until September.

The plant reaches its peak growth and biomass shortly after flowering, when milfoil stems begin to branch and form dense clusters, blocking available sunlight to other submerged plants. Soon after this peak biomass in late summer to early fall the plant begins a natural process called auto-fragmentation, whereby small branches begin to develop roots, break away from the parent plant, and float until they lose buoyancy, at which point they sink and root in the sediment, ultimately forming new plants.

Eurasian water-milfoil has been confirmed in 18 lakes in the Greater Sudbury area, Nepahwin Lake being one of them. Once established, EWM is extremely difficult to control as it forms dense mats that can overwhelm native plant communities present within the lake.

  • Reduces biodiversity by competing with native aquatic plants and reducing suitable fish habitat.

  • Decomposition of EWM reduces oxygen levels in the water that can lead to fish kills.

  • Dense areas of EWM can cause problems for recreational activities such as boating, swimming and fishing and decreases the esthetic appeal of the lake.

  • Researchers  in Washington state  found that EWM in lakes had a significant negative effect on property sales prices, corresponding to a 19% decline in mean property value. 


You do not need a work permit under the Public Lands Act, if you can follow all of these rules. You:

  1. are the waterfront property owner or conducting work on behalf of the property owner

  2. minimize the removal of native aquatic vegetation (e.g., wild rice)

  3. dispose of the plants/material you remove on dry land to prevent it from re-entering the water

  4. use, operate or store any wheeled or tracked machinery/equipment on dry land, or on a barge or vessel

  5. do not carry out work during fish spawning season or during the time of other critical fish life stages, as set out in the In-water Work Timing Window Guidelines. Nepahwin Lake supports pike and smallmouth bass, leading to in-water work being restricted from April 1-July 15.

Best management practice states:

  1. use your hands to remove the entire plants, including roots and rhizomes. This will probably require a snorkeller or scuba diver, along with a partner on a raft to collect loose fragments and the pulled plants. Fragmentation of the plant by mechanical devices  (e.g. rakes, cutter bars) can lead to further spread. Do not dredge the bed of the waterbody.

Simkovic, Vicki. 2020. Eurasian Water-Milfoil (Myriophyllum spicatum): Best Management Practices in Ontario. Ontario Invasive Plant Council, Peterborough, ON.



In 2011 the City of Greater Sudbury (CGS) retained the services of EnviroScience Inc. for a 3-year contract to conduct biological control of EWM on six lakes (Grant, Simon, McFarlane, Long, Richard, St Charles) using the native Milfoil Weevil. Mapping of aquatic species done on 5 of the 6 lakes in 2014 showed some effect, but a number of issues led to this project not continuing.


In 2017 the Greater Sudbury Watershed Alliance (GSWA) explored the use of benthic (bottom of a body of water) mats. The permanent placement of jute mats had been used in research projects in Quebec and Southern Ontario. However, the Ministry of Natural Resources and Forestry had concerns about the disruption to the natural benthic invertebrates and flora and the biodegradation of the permanent jute mat, so the project did not proceed.


In 2019, led by Dr. Charles Ramcharan, School of the Environment, Laurentian University (LU) and supported by 3 LU students and members of the Sudbury Dolphin Aquatic Club, the GSWA Eurasian Water-Milfoil Aquatic Invasive Species (EWM-AIS) subcommittee embarked on a research project entitled Lake Aquatic Invader Control in Sudbury (LAICS). LAICS test sites are in Long, Richard, Ramsey and St Charles Lake. LAICS used seasonally installed inert 8’ X 8’ Geotextile mats at 18 study sites. This project was ongoing in 2020 at some sites and some preliminary results were promising. However, as of 2021, the status of residents being able to obtain a permit to lay down benthic mats on the lake bottom in front of their home is still not resolved.


In 2020, Bill Querney joined GSWA-EWM-AIS sub-committee to represent the Nepahwin Lake Watershed Stewardship Group in future initiatives to control EWM. Bill is passionate about keeping Nepahwin Lake beautiful for all of us to enjoy for many years to come.

Feel free to Contact Us with your thoughts. 

Olden JD, Tamao M. Incentivizing the public to support invasive species management : Eurasian milfoil reduces lakefront property values. PLoS One. 2014; 9(10) e110458 online

Simkovic, Vicki. 2020. Eurasian Water-Milfoil (Myriophyllum spicatum): Best Management Practices in Ontario.

Ontario Invasive Plant Council, Peterborough, ON.

CGS Aquatic Vegetation and Eurasian Milfoil Preliminary Survey

Long Lake Stewardship Controlling the Milfoil Zombie

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