Log in

Milfoil Control on Lake St. Catherine


Eurasian watermilfoil is a non-native aquatic plant that is present in most U.S. states and much of Canada. This plant is known for its rapid growth and ability to spread, which can lead to significant problems within a lake. Milfoil forms dense beds that can seriously impair the recreational use of a lake, reduce the availability of fish spawning grounds, outcompete beneficial native plants, and otherwise alter a lake’s natural environment.

The growth and spread of Eurasian watermilfoil is a threat to all our lakes and ponds. Once Eurasian watermilfoil has infested a lake and becomes established, it can be impossible to eradicate it. Lake managers can only seek to control it by integrating the most effective, economically feasible, and environmentally sound methods available.

Of note, Shadow Lake which discovered milfoil plants in 2011, were able to eradicate it after 5 years of intense efforts. Prevention of milfoil introduction to a lake via Greeter Programs and early detection of milfoil plants are critically important to prevent the spread of milfoil. After milfoil was newly discovered in Shadow Lake, their lake association got to work using numerous methods over many years to eradicate their small population of milfoil before it became established and spread throughout the lake.

A drawing and a photograph of Eurasian Watermilfoil, EWM, milfoil.

Milfoil was introduced into Lake St. Catherine in the early 1970s, and it quickly spread around the lake. With milfoil increasingly becoming an issue, in 1979, the LSCA purchased a mechanical harvesting machine (many lake old-timers will remember “Hungry Harvey”). This was the only form of milfoil “control” at the time. After many years of using mechanical harvesting machines, it was determined that the cutting of the milfoil was actually contributing to its spread around the lake because of the fragmentation created, and other control options were explored.

The Vermont Agency of Natural Resources had this to say about mechanical harvesting Eurasian watermilfoil:

"...this method did not provide a satisfactory level of control and may have contributed to its spread via fragmentation. Experience with mechanical harvesting on Rutland County lakes in the 1980’s and 1990’s showed that harvesting resulted in dense beds of EWM since the aggressive plant is quickest to regrow after cutting." - Permit Response #2014-C01

The LSCA stopped mechanically harvesting milfoil in 2003.


Eurasian watermilfoil is not native to North America but originates from Europe, Asia and northern Africa. As an aquatic invasive species (AIS) to this continent, Eurasian watermilfoil has no natural controls (insects, bacteria, fungi) to keep its growth in check. Milfoil stems can reach the surface in up to 20 feet of water, growing up from the lake bottom each year from a fibrous root system. Milfoil grows and spreads extremely quickly, forming dense surface mats. Eurasian watermilfoil will grow readily in many types of lakes, as well as on almost any lake bottom type: silty, sandy, or rocky.

The presence of Eurasian watermilfoil often brings a change in the natural lake environment. Over time, it outcompetes and suppresses the more beneficial native aquatic plants, severely reducing natural plant diversity within a lake. Since its growth is typically dense, milfoil weed beds are poor spawning areas for fish. Although many aquatic plants serve as valuable food sources for wildlife, waterfowl, fish, and insects, Eurasian watermilfoil is rarely used for food. Dense surface mats of milfoil can also impede recreational activities like fishing, boating, kayaking, and swimming.

Eurasian watermilfoil reproduces almost exclusively by the breaking off of fragments which can drift away, sink, develop roots, and grow into plants. A fragment just a few inches long is capable of starting a new plant. This fragmentation occurs both naturally and as a result of human activity. Within a lake, wind and waves may break plants loose, allowing them to drift into new locations and root. Boating activity through dense milfoil beds also contributes to the fragmenting and spread of milfoil plants.

From USGS.gov:

“Eurasian watermilfoil competes aggressively to displace and reduce the diversity of native aquatic plants. It elongates from shoots initiated in the fall, beginning spring growth earlier than other aquatic plants. Tolerant of low water temperatures, it quickly grows to the surface, forming dense canopies that overtop and shade the surrounding vegetation (Madsen et al. 1991). Canopy formation and light reduction, are significant factors in the decline of native plant abundance and diversity observed when Eurasian water-milfoil invades healthy plant communities (Smith and Barko 1990; Madsen 1994).”

From the Lake Champlain Basin Program (LCBP), milfoil can:

    • Decrease native plant diversity by out-competing native aquatic plants
    • Decrease light penetration, habitat complexity and oxygenation
    • Increase sedimentation, nutrient loading, and accelerate eutrophication
    • Affect PH and temperature levels

When milfoil was introduced into Lake St. Catherine, it quickly spread throughout the littoral zone of the lake (the area of the lake that supports rooted aquatic vegetation), out-competing our native plants, and impacting the health of the lake.

Here is an image from Little Lake taken in early June of 2021. Because of its shallow depth, the whole of Little Lake is a littoral zone. You can see how dense the milfoil can grow, and how it had taken over Little Lake:

A photo of Little Lake showing dense milfoil growth


The LSCA’s Milfoil Control Program consists of four components:

1. ‘Stop The Spread’ education and outreach. Our ‘Stop The Spread’ campaign educates boaters and property owners on best practices to limit the spread of milfoil. Each year, the LSCA holds a lake community meeting to discuss the control plan for the season, answer questions, and hand out a flyer with best practices for lake users to limit the spread of milfoil.

A 'Stop The Spread' flyer from 2023

2. Volunteer milfoil cleanup. Throughout the season, we organize volunteers to collect detached floating milfoil from the lake and deposit it on our designated drop off platforms. The milfoil is then picked up from the platforms and disposed of. We also encourage boaters and property owners to remove any milfoil they see in the lake while boating or on their shoreline.

Volunteer milfoil drop-off float

3. DASH - Diver Assisted Suction Harvesting. Our DASH crew suits up in scuba gear and hand-pulls milfoil by the roots from the lakebed. In sections of lower milfoil density, they will swim the area and hand-pull with mesh bags. In higher density areas, they will set up the DASH equipment which allows them to suction the hand-pulled milfoil up through a tube to a catch table on a boat. Milfoil is then placed in 17.5 gallon buckets for transport off the lake.

The Lake St. Catherine Association's Diver Assisted Suction Harvesting (DASH) crew

Video of our DASH team working underwater:

4. Herbicide spot treatments with ProcellaCOR EC. In order to maximize our DASH crew’s time, effectiveness, and number of acres covered, one of our control methods includes spot treatments with the herbicide ProcellaCOR EC. We’ll further discuss ProcellaCOR later in this article. When the lake is spot treated by herbicide, the State recommends that the lake not be used for any purpose on the day of the treatment. Normal recreational and domestic (household) lake water use may resume the next day after treatment, and use of lake water for irrigation may resume 1 week after the treatment.

Although not directly related to Milfoil Control, the LSCA's work on Lake Wise on LSC, the LSC Stormwater Master Plan, and the LSC Watershed Action Plan all help to limit phosphorus and other nutrients from entering the lake which can contribute to excessive plant growth, and improves overall water quality.

These efforts have resulted in the lowest percentage of milfoil cover and frequency of occurrence in the lake since the mid-2000s. Also, and just as importantly, we have seen many species of our native aquatic plants that have been suppressed by milfoil growth like Water stargrass, Tape grass, Thin-leaf pondweed, Illinois pondweed, Common waterweed, and Robbins’ pondweed have all increased in frequency of occurrence. You can view our Aquatic Vegetation Management Reports dating back to 2001 here.

These results are exactly what we want to see!

Lake St. Catherine has over 30 native aquatic plants which are important and necessary to sustain a healthy lake ecology. Our efforts are focused on reducing the amount of milfoil in the lake so that these native aquatic plants can grow as they normally would. Keeping milfoil under control is helping to return the aquatic plant environment to conditions before milfoil was introduced in the 1970s. Because of our milfoil control efforts, we again have a complex and diverse native aquatic plant community.

For example, here is video of our DASH team evaluating the results of a small spot treatment two months after it was performed in Forest House Bay in mid-June of 2022:

As anticipated, no milfoil was observed, and you can see that our native plants like Eelgrass, Illinois pondweed, and Robbins' pondweed are healthy and abundant.

It’s also important to note that our Boat Launch Greeter Program is a crucial part of invasive species prevention. Although we already have milfoil in Lake St. Catherine, other Vermont lakes do not. Our Greeters who are on duty at the Boat Launch in Wells, and the State Park in Poultney, check boats and trailers to make sure they do not have milfoil on them when they leave. They also check boats and trailers entering the lake for other invasive species that are not currently in LSC like zebra mussels, spiny waterflea, asian clams, and water chestnut which are only a lake away.


In late September, our lake management contractor (SOLitude Lake Management) performs a comprehensive, two day aquatic plant survey. They visit the 199 GPS data points that were set up in 2001 to evaluate the aquatic plants observed at these locations. Using the data collected, and recommendations from our DASH team based on their observations from the season, our team creates a preliminary control plan of areas to be hand-pulled / suction harvested or spot treated with ProcellaCOR.

In January, the LSCA meets with the Vermont DEC to review the work of our Milfoil Control Program for the previous year, and discuss our preliminary plans for the upcoming year. This meeting is also a great opportunity to discuss our other lake and water quality improvement programs with the DEC.

Then, in early May, both SOLitude and our DASH team will perform a spring survey and compare it to the fall survey. A final plan will then be created and submitted to the DEC for approval. The LSCA will then inform the lake community of our finalized plans for the season with direct mailings, emails, announcement posts on our website and Facebook pages, and with signage around the lake. We will also schedule a meeting for the lake community so we can discuss the plans for the season, present best practices to limit the spread of milfoil, and answer questions.


In May of 2022, as part of our Spring 2022 Newsletter, we noted that misinformation was being posted online and in newspaper commentaries related to the Lake Bomoseen Association applying for a permit to use the herbicide ProcellaCOR EC to control Eurasian watermilfoil. ProcellaCOR is the product that we have used as part of our Milfoil Control Program for spot treatments since 2019. As we mentioned then, and has continued to occur, some are even making things up and disparaging Lake St. Catherine, then using these false stories to voice their opposition to the use of ProcellaCOR.

To help combat this misinformation, and to provide fact-based information on ProcellaCOR, the Vermont Department of Environmental Conservation (DEC), Watershed Management Division, Lakes and Ponds Management and Protection Program published a document in October of 2022 entitled “Permitting Aquatic Herbicide Projects in Vermont”.

The Vermont DEC describes that the purpose of this document is to:

1. Provide background information about DEC’s Aquatic Nuisance Control (ANC) permitting program, with a specific focus on aquatic herbicide projects;

2. Identify some of the recent findings related to ProcellaCOR; and

3. Provide a Q&A section on this topic reflecting common questions that DEC receives about our ANC permitting program

Permitting Aquatic Herbicide Projects in Vermont - a document from the Vermont DEC

The document details Vermont statutes, the permitting application and technical review process, and the departments and agencies involved in the permitting process.

It also discusses key findings on ProcellaCOR EC, including:

    • a pre- and post-treatment statistical analysis of the aquatic plant survey data from Vermont treated waterbodies (showing increases in native plants, and decreases in milfoil)
    • an Aquatic Toxicity Review memorandum performed by a DEC Environmental Scientist (concluding that "the potential for acute and chronic risks to fish, aquatic invertebrates, amphibians and other aquatic animals is considered low")
    • a Macroinvertebrate Survey conducted by the New York DEC (finding that "No significant changes to the macroinvertebrate community assemblage were observed when comparing survey results pre- and post-herbicide treatment.")
    • a review of ProcellaCOR’s confidential statement of formulation memorandum performed by a Vermont State Toxicologist from the Vermont Department of Health (concluding: "Based on a review of the confidential statement of formulation, it is reasonable to conclude that human exposure to the inert compounds contained in ProcellaCOR at the concentrations that would result under the conditions proposed by the applicants, is not likely to result in an increase in the level of concern for public health. Thus, the proposed treatment of Lake Bomoseen with ProcellaCOR is expected to result in negligible risk to public health, from both the active and inert compounds in ProcellaCOR.")
    • an acknowledgement from the DEC’s Drinking Water & Groundwater Protection Division ("DWGWPD does not have concerns with the use of ProcellaCOR provided the conclusions from VDH have not changed and that treatment concentrations do not exceed 5 PDUs.")
    • …and much more.

Finally, the document contains 16 frequently asked questions posed to the DEC about these topics with their answers.

This document can be viewed here: Permitting Aquatic Herbicide Projects in Vermont

Additional inks:

As you will read on the specimen label, there are two plants that are native to Lake St. Catherine that can be affected by ProcellaCOR: Watershield and Coontail. Knowing this, efforts and decisions were made to mitigate the impact on these species by working to keep milfoil spot treatments away from populations of these natives. While we have noted a decrease of these natives near spot treatment areas, they have, and continue to rebound. For example, when Lily Pond was spot treated in 2020, Coontail was not seen at the 24 GPS data points there. This does not necessarily mean that it was no longer in Lily Pond - just that it was not found in the late September survey of 2020 at the any of the 24 GPS points. However, Coontail has rebounded and has increased in frequency of occurrence in 2021 and 2022. We will continue to work with the DEC to make sure future treatments limit or do not impact non-target species.


First and foremost, your financial support in the form of the yearly dues you contribute to the LSCA are crucial to help fund this program. If you are not currently a member, please consider joining! You can do so easily via our website here: Become A Member, or you can click here to: Make A Donation.

Help to make these efforts a success:

Here are the things that you can do to help stop the spread of milfoil, which are all applicable lake-wide. All require a bit of elbow grease on your part, but if we are all contributing, it can make a big difference around the lake.

  1. As a general rule, get as much milfoil out of the lake as possible. Let it dry out on land and dispose of it as you would yard waste.
  2. Don’t drive through milfoil patches with your boat which will create fragments.
  3. If you have milfoil on your prop, don’t just reverse and drive away, please remove it from the lake.
  4. If you have milfoil growing in your dock or swimming area, pull it out by the roots and remove it from the lake.
  5. If you see milfoil floating anywhere in the lake, near your dock, or along your shoreline, remove it from the lake.
  6. Obey boating regulations by travelling at no-wake, 5 MPH speeds within 200’ of the shoreline.

Keep in mind that native aquatic plants are important and necessary to sustain a healthy lake ecology. Please focus on removing milfoil plants only.

It's up to all of us to stop the spread of milfoil.


The four components of our Milfoil Control Program have been very successful in both keeping the milfoil in check, and in allowing our native aquatic plants to thrive - creating a healthy ecosystem for LSC’s fish and wildlife, and a beautiful lake for all of us to enjoy.

Milfoil Control is just one of the numerous water quality programs the LSCA works on each year. Other programs include: the LSC Stormwater Master Plan, the Lake Wise Program, the LSC Watershed Action Plan, and current and future water testing and measurement programs. These water quality improvement projects are funded by grants earned by the LSCA, allocations from the towns of Wells and Poultney, and your membership contributions and donations.

The LSCA has always employed evidenced-based decision making when evaluating lake related issues, and we continue to do so with our Milfoil Control Program. Working with the State and lake scientists & experts, following the science and the data, and evaluating the results of our efforts show that we are doing the right things for the long-term health of Lake St. Catherine.

To our members, and all who love Lake St. Catherine, if you ever have any questions or concerns, reach out to us. We would be happy to discuss our Milfoil Control Program or any other lake related topic with you so we can address your questions or concerns, and provide you with factual information. Or contact us, and we’ll set up a Dockside Chat, and a LSCA Trustee will swing by your dock for a chat about the lake.

You can always reach us at info@lakestcatherine.org.

 Vermont DEC Agency of Natural Resources logo.

Support provided in part by

Vermont Department of Environmental Conservation

Vermont conservation license plates 

This Lake St. Catherine Association project is made possible by a grant earned from the Lake Champlain Basin Program & NEIWPCC, and is partially funded by the US EPA.


Search lakestcatherine.org:

Lake St. Catherine Association
PO Box 631
Wells, VT 05774

Follow us on:

Powered by Wild Apricot Membership Software