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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. Commonly found in shallow bays and along the shoreline, 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 there is no known way to eradicate it. Lake managers can only seek to control it by integrating the most effective, economically feasible, and environmentally sound methods available.

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


Eurasian watermilfoil is not native to North America but originates from Europe, Asia and northern Africa. As an "introduced" invasive species to this continent, Eurasian watermilfoil has no natural controls (insects, bacteria, fungi) to keep its growth in check. In North America it has the potential to completely infest lakes once introduced. Native types of watermilfoil rarely attain such extensive growth.

Eurasian watermilfoil 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. Unlike most native aquatic plants, which are usually associated with particular water qualities, 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 may outcompete or eliminate 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 and may lead to populations of stunted fish. Although many aquatic plants serve as valuable food sources for wildlife, waterfowl, fish, and insects, Eurasian watermilfoil is rarely used for food. Commonly found in shallow bays and in bands along the shoreline, dense surface mats of milfoil can also make fishing, boating and swimming virtually impossible.

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.


Human recreational activities usually account for the spread of non-native aquatic plants and animals between lakes. Fragments of aquatic plants cling to the propellers of boat motors or to boat trailers and, if not removed, can start new populations when the boat is launched into another waterbody. Unfortunately, once Eurasian watermilfoil has been introduced into a lake, there is no way to completely eradicate it.

To stop the further spread of non-native aquatic species, it is imperative that all plant fragments are removed from boats before putting in or leaving a lake's access area. Removed plant material should be properly disposed of in a trash receptacle or on high, dry ground where there is no danger of them washing into any waterbody.

It is illegal to transport Eurasian watermilfoil, water chestnut, zebra mussels or quagga mussels to or from any Vermont surface water. Any person found transporting these species to or from a Vermont lake or pond will be in violation of this law (10 V.S.A. ยง 1454).


Since there is no way to completely eradicate Eurasian watermilfoil from a lake once it has been introduced, control efforts must instead focus on: controlling newly introduced infestations, preventing further spread of the plant, or reducing the nuisance level of the problem. Some methods are more appropriate for well-established populations, while others are better suited for those that are recent introductions.

Since the mid 2000s, the Lake St. Catherine Association has successfully controlled milfoil in Lake St. Catherine using a balanced approach of DASH (Diver Assisted Suction Harvesting) and spot treatments of herbicide.

Each season, our suction harvesting team and our lake management contractor (SOLitude Lake Management) perform a Spring and Fall milfoil survey. Using the GPS mapping data collected, our team creates a control plan to include areas to be suction harvested or spot treated with the herbicide ProcellaCOR. For example, for the 2020 season, we treated approximately 18.3 acres with herbicide and 38.7 acres will be suction harvested.

When the lake is spot treated by herbicide, it is recommended 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.

You’ll see our DASH team working throughout the summer. They hand pull the milfoil from the bottom of the lakebed by the roots and then suction the full plant to the surface for safe removal from the lake.

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

Video of our DASH team working underwater:

Before this successful plan of spot treatments and suction harvesting began, the LSCA used mechanical harvesting machines (beginning in 1979). Many long-time LSC residents will remember "Hungry Harvey" chewing through the milfoil around the lake. After years of harvesting the milfoil, the LSCA realized that mechanical harvesting was spreading the milfoil around the lake. During the harvesting, only up to 4 feet of the milfoil bed is cut and small milfoil fragments are created. These fragments can float away and create whole new beds of milfoil. Milfoil also regrows very quickly after being cut.

The Vermont Agency of Natural Resources has this to say about mechanical harvesting Eurasian watermilfoil (EWM):

"...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.


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.

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

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