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Plant guide · Submerged plants

Eurasian watermilfoil (Myriophyllum spicatum)

An invasive underwater plant with feathery leaves in whorls of four or five. Its stems reach the surface and branch into a thick canopy. Penn State says to eradicate it as soon as you see it.

Also called: Eurasian water-milfoil, milfoil

A single Eurasian watermilfoil stem with feathery reddish leaves over a gravel lake bottom.
Eurasian watermilfoil, showing its feather-like leaves. Photo: Tigerente, CC BY 4.0 (source)

What it looks like

  • Long stems reaching the surface, with feather-like leaves in whorls of four or five.
  • Stems branch at the surface into a dense canopy.
  • Each leaf has more than fourteen divisions; native northern watermilfoil has fewer (Penn State).
  • Spreads mainly from stem fragments.

Easily confused with

  • Native northern watermilfoil: fewer leaf divisions and rarely a nuisance.
  • Coontail: spiny, forked leaves rather than feathery ones.

Good and bad for your pond

  • Gives some habitat, but its fast growth quickly outweighs any value.
  • Dense surface mats interfere with pond use and can drop summer oxygen enough to kill fish.

Native or invasive?

Pennsylvania noxious weed

Invasive; Pennsylvania noxious weed. Class B noxious weed in Pennsylvania (PDA), a severe-threat invasive on DCNR's list, and one of PFBC's 'least-wanted' aquatic invasive species; introduced (USDA PLANTS).

USDA PLANTS: MYSP2 (lower 48 states: introduced)

Noxious weeds (e.g. water chestnut, hydrilla, Eurasian watermilfoil) may not be sold, moved or planted in PA.

Checked Oct 4, 2026 · Source: Controlled Plant & Noxious Weed Lists This may be outdated

Do grass carp eat it?

Grass carp eat it

PFBC lists watermilfoil among grass carp foods, but Penn State says grass carp rarely eat enough to keep it under control. Grass carp prefer submerged plants like pondweeds, elodea and coontail; they rarely control algae mats or lilies.

Checked Oct 4, 2026 · Source: Using Grass Carp to Control Aquatic Plants (updated May 19, 2025) This may be outdated

Control options

Prevention first

Noxious weeds (e.g. water chestnut, hydrilla, Eurasian watermilfoil) may not be sold, moved or planted in PA. Penn State Extension's advice for every nuisance plant and algae problem starts with nutrients: overgrowth is a symptom of excess phosphorus and nitrogen from sources such as barnyards, crop fields, septic systems, lawns and golf courses. Cutting fertilizer near the pond, maintaining septic systems, diverting nutrient-rich runoff and keeping a vegetated buffer strip are the long-term fixes; without them, control becomes a yearly chore.

Checked Oct 4, 2026 · Sources: Controlled Plant & Noxious Weed Lists; Filamentous Algae (updated May 19, 2025) and the companion Penn State plant fact sheets This may be outdated

Remove it by hand or machine

Cutting or raking isn't recommended: fragments root and spread. A winter drawdown can freeze the roots: Over 1 acre (or with another state permit): PFBC drawdown permit, 30+ days ahead, no fee.

Checked Oct 4, 2026 · Source: Apply to Draw Off Water from Impoundments This may be outdated

Biological options

Grass carp give limited control (see above).

Chemical options (permit first)

Any herbicide or algaecide in a pond needs a joint DEP/PFBC Chapter 91 permit first, at any amount. Only products registered with the U.S. Environmental Protection Agency and with the Pennsylvania Department of Agriculture, and labeled specifically for aquatic use, can be listed on the Chapter 91 permit application. Treat in sections, early in the season: decaying plants can strip oxygen and kill fish.

Checked Oct 4, 2026 · Sources: Water Quality Permitting for Pesticide Applications in Pennsylvania: FAQ (rev. Feb 21, 2025), FAQ #2, #3, #8, #10, #11, #28, #29; Permit Requirement for Use of an Aquatic Herbicide in Ponds (updated Sep 8, 2025); Pond Management (FAQ: controlling submerged vegetation) This may be outdated

Follow the product label; the label is the law. A Chapter 91 permit is required before any herbicide or algaecide goes in a pond (see fact). Consider a licensed applicator.

Report it

Report a suspected aquatic invasive species, such as hydrilla or European water chestnut, to the Pennsylvania Fish and Boat Commission with its online form or the Pennsylvania Invasive Species Reporting hotline (1-833-INVASIV), or through PA iMapInvasives. A photo and the exact location help staff confirm it.

Checked Oct 4, 2026 · Source: Report Aquatic Invasive Species (AIS) This may be outdated

PFBC: Report aquatic invasive species PA iMapInvasives

Sources

Checked Oct 4, 2026