Eurasian Watermilfoil in Wisconsin
As of September 2026: Eurasian watermilfoil is a restricted invasive species under Wis. Admin. Code NR 40. This page summarizes current DNR guidance; confirm identification before treating anything as exempt.
Eurasian watermilfoil is the invasive plant most Wisconsin lakefront owners have already heard of, and it's also the one most often confused with a native lookalike. Getting the identification right matters here more than with almost any other plant, because Wisconsin gives invasive species an easier removal path than native ones, and pulling the wrong plant by mistake is still a violation.
How to identify it
Eurasian watermilfoil
invasiveMyriophyllum spicatum
- Feathery leaves in whorls of 4 around the stem
- Each leaflet divided into 12 or more pairs of thin segments
- Stem runs 3 to 10 feet, often reddish and limp out of water
Restricted invasive. Hand removal is permit-exempt statewide; chemical treatment needs an NR 107 permit.
Identification only. Permit rules are on the DNR permit page.
Native watermilfoil
nativeMyriophyllum sibiricum
- Looks like Eurasian watermilfoil at a glance
- 10 or fewer leaflet pairs per leaf, versus 12 or more
- Stiffer stalks, not limp or reddish out of water
Easy to mistake for the invasive lookalike. Confirm the leaflet-pair count before pulling; removing native milfoil without an exemption is a violation even by mistake.
Identification only. Permit rules are on the DNR permit page.
The count that separates them: Eurasian watermilfoil carries 12 or more thin leaflet pairs per leaflet, while the native milfoil usually has 10 or fewer, with a stiffer, less reddish stem. When you can't count leaflets confidently from the shore, treat the plant as native until you can confirm otherwise.
Why it matters
Eurasian watermilfoil forms dense surface mats that shade out native plants, crowd swim areas and boat lanes, and spread easily. A single fragment can root and start a new colony, which is why the state classifies it as a restricted invasive species under NR 40 and why boat landings post inspection and cleaning reminders. Left alone, a small patch at one dock can become a lake-wide problem within a few growing seasons.
Control options
- Hand-pulling. Confirmed Eurasian watermilfoil can be hand-removed along your shoreline without a DNR permit, unlike native plants, which are capped at a 30-foot corridor. Get the root out, not just the stem, since fragments can re-root.
- Herbicide. Chemical treatment under NR 107 needs a permit every season and is typically how lake districts handle larger infestations. It's not selective for a single plant near your dock; nearby native plants can be affected too.
- Mechanical harvesting. Cutting and collecting milfoil by machine covers more area than hand-pulling but leaves fragments behind unless collection is thorough, and it needs a permit.
- DASH (diver-assisted suction). A slower, selective option that removes individual plants by hand underwater while a diver directs a suction hose, useful where native plants are mixed in and you want to avoid pulling them too.
Full cost ranges for each method are on the cost comparison page.
Permit path
Hand removal of Eurasian watermilfoil is exempt statewide under the DNR's invasive-species removal allowance, so a homeowner can pull it by hand at any width along their own shoreline without applying first. Herbicide treatment always needs an NR 107 permit, no matter how small the patch, and mechanical harvesting beyond the small-waterbody exemption needs an NR 109 permit. If milfoil covers more than a dock-side patch, most lakes handle it through a lake-association aquatic plant management plan rather than a single owner's application; see how a lake-wide plan gets approved.
Full decision-tree logic for permits is on the DNR permit rules page.
Don't confuse it with these
Native watermilfoil looks similar enough that the DNR flags it as the top misidentification risk in the state. Coontail also gets mistaken for milfoil at a glance, though its leaves are forked and stiff rather than feathery. See the coontail identification guide and curly-leaf pondweed, the other common invasive, for the full comparison.