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The plant behind the “invasive species nobody is talking about” headline is variable-leaf watermilfoil (Myriophyllum heterophyllum). It can spread when plant fragments hitchhike on boats and trailers, then form dense mats that interfere with boating, fishing, and swimming. The practical response is to keep fragments out of new waters and avoid releasing aquarium or pond plants outdoors.
What is variable-leaf watermilfoil?
Variable-leaf watermilfoil is a submerged aquatic plant with feather-like leaves arranged in whorls around its stems. In mid to late summer, a spike-like flower rises above the water. It is often found along lake and pond shorelines, and can form dense mats near the surface in water as deep as 10–12 feet, according to Maine Department of Environmental Protection guidance.
The species is Myriophyllum heterophyllum. USGS describes it as native to parts of the United States, but nonindigenous in places beyond its historical range. The common name “watermilfoil” covers multiple plants, including native species, so a suspected sighting should be checked against a state identification guide or local aquatic invasive species program rather than identified from a quick glance.
Why does the headline say nobody is talking about it?
That phrase is a rhetorical framing from a Treehugger article updated October 11, 2018—not a measured finding about public awareness. The article identifies variable milfoil as its subject, but the available sources do not establish how widely the public knows about it. The plant’s practical significance is clearer than any claim about how much attention it receives.
How does it spread?
Fragments can start new growth
Variable watermilfoil reproduces primarily by fragmentation. Pieces can break off through wave action caused by boats, swimmers, or animals, and fragments can be carried to another part of a waterbody. That makes careless movement of plant material a concern even when a boat leaves a lake that appears clear.
Boats, trailers, and released plants move it between waters
USGS lists aquarium or pond plant releases as an introduction pathway and boats or trailers as possible secondary spread routes. New Hampshire DES described fragments attached to boats or trailers as a likely route into the state’s waters. Waterfowl are also listed by USGS as a possible secondary pathway.
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What damage can it cause?
As mats thicken near the surface, they can make boating, fishing, and swimming difficult. Maine DEP also identifies reduced water quality as a concern; New Hampshire DES describes effects on native aquatic vegetation. These are ecological and recreational concerns, not evidence that every infestation has the same severity.
Extent figures need a date and place attached. New Hampshire DES reported variable milfoil in over 75 state waterbodies in its 2019 factsheet; that is not a current count or a national total. USGS occurrence records include California, Connecticut, Maine, Massachusetts, Rhode Island, Texas, Vermont, and Washington, but the profile cautions that recorded populations may no longer be present. Its records, last updated September 6, 2026, are occurrence evidence—not a live map of confirmed infestations.
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How can boaters and aquarium owners help stop its spread?
- Before leaving the water: Inspect the boat, trailer, and equipment for attached plants or fragments. Check areas where vegetation can catch, including propellers, axles, and bunks.
- Remove visible plant material: Clean off fragments and follow local instructions for cleaning, draining, and disposing of them. Do not move removed plants to another waterbody or dump them where runoff could return them to the water.
- Do not release aquarium or pond plants: Never empty unwanted plants into lakes, ponds, streams, or storm drains. Follow local guidance for safe disposal.
- Check local rules: Cleaning, drainage, and disposal requirements can vary by jurisdiction. A brush or aquatic invasive species cleaning kit may help remove visible fragments, but equipment alone does not guarantee decontamination.
Rules are not uniform nationwide. For example, Maine DEP says listed invasive aquatic plants, including nonindigenous Myriophyllum species, are illegal to sell, propagate, or introduce to Maine waters. Maine’s restriction is state law, not a national rule.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.What if it is already established?
Prevention matters because established infestations can be difficult to eliminate. Maine DEP puts it plainly: “Once introduced into a lake, variable watermilfoil is virtually impossible to eradicate.” That warning does not mean management cannot reduce impacts; it means eradication should not be assumed.
Control choices depend on the site, local permits, and potential effects on native plants and water quality. The available sources do not establish a universally best method or comparable current costs and effectiveness for herbicides, harvesting, or hand removal. Report a suspected infestation to your state aquatic invasive species program or lake-management authority, and ask them about identification, permits, and site-specific options before attempting control.
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