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Plant guide · Floating plants

European water chestnut (Trapa natans)

An invasive annual that forms floating rosettes of glossy, toothed, triangular leaves and drops sharp four-spined nuts. It is spreading in Pennsylvania and is on the state's noxious weed list.

Also called: water chestnut

Floating rosettes of toothed, triangular water chestnut leaves covering dark water.
European water chestnut rosettes. Photo: Agnieszka Kwiecień, Nova, CC BY-SA 4.0 (source)

What it looks like

  • Floating rosettes of glossy, roughly triangular leaves with toothed edges.
  • Feathery leaves underwater along a long, cord-like stem.
  • Small white four-petalled flowers in the center of the rosette from mid to late July.
  • Hard nuts with four sharp spines, ripening about a month after flowering; spines can puncture shoes.

Easily confused with

  • Penn State says no other aquatic plant is a real look-alike.

Good and bad for your pond

  • Little food value for wildlife compared with native plants.
  • Dense mats choke ponds, block light, lower oxygen and make fishing, boating and swimming nearly impossible.
  • Seeds can stay viable for many years, so an infestation takes years to clear.

Native or invasive?

Pennsylvania noxious weed

Invasive; Pennsylvania noxious weed. Class A noxious weed in Pennsylvania (PDA) and a severe-threat invasive on DCNR's list; introduced to North America (USDA PLANTS). Penn State reports its Pennsylvania range is expanding.

USDA PLANTS: TRNA (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Checked Oct 4, 2026 · Source: Controlled Plant & Noxious Weed Lists This may be outdated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?

Not on PFBC's grass carp list

Not on PFBC's grass carp list.

Control options

Prevention first

Noxious weeds (e.g. water chestnut, hydrilla, Eurasian watermilfoil) may not be sold, moved or planted in PA. Clean, drain and dry boats and gear between waters.

Checked Oct 4, 2026 · Source: Controlled Plant & Noxious Weed Lists This may be outdated

Remove it by hand or machine

Catch it early: hand-pull small patches in late spring or early summer, before seeds form, remove every rosette, and bag the plants for disposal far from water. Watch the pond for several years.

Biological options

None.

Chemical options (permit first)

Larger infestations may need an herbicide. 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.

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) 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