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Water Chestnut (Trapa natans)

Water chestnut (Trapa natans) is a rooted submerged aquatic plant that quickly forms dense floating mats and outcompetes native plant communities. Its decay can deplete oxygen levels, leading to fish kills. Dense growths can interfere with swimming and entangle propellers, which hinders boating, fishing, and waterfowl hunting. In mid-July, small white flowers appear on rosettes at the water's surface. When fruits form, they become submerged and dangle beneath the rosettes. These woody chestnuts develop four sharp spines and wash ashore where they can be hazardous for swimmers and walkers, and can even puncture bike and ATV tires.

Native to Europe, Asia and Africa, water chestnut was first discovered in North America in the late 1800s, imported as a showy water garden plant. It escaped to New Hampshire, Connecticut, Massachusetts, New York, Vermont, and Rhode Island. It spreads by rosettes, woody seeds, and plant pieces that break off and float on water currents. Water chestnut can spread to new waters through improper disposal by water gardeners and by clinging to watercraft. Controlling established water chestnut infestations is costly. Your actions and your help in reporting new infestations are vital for preventing their spread.

Identify Water Chestnut

Identify Water Chestnut

General Characteristics

  • Rooted plant with floating leaves that form impenetrable mats at water surface
  • Mats impair recreation in lakes, ponds, and moderately flowing rivers
  • Each chestnut contains 25 seeds; 1 acre can produce seed to cover 100 acres the next year

What You Can Do

  • Learn to recognize water chestnuts.
  • Clean all aquatic plants, animals and mud from watercraft, trailers, docks, lifts, anchors and other recreational equipment before leaving access.
  • Drain water-related equipment (boat, ballast tanks, portable bait containers, motor) and drain bilge, livewell and baitwell by removing drain plugs before leaving water access. Keep drain plugs out while transporting watercraft.
  • Dispose of unwanted bait, worms and fish parts in the trash.
  • Spray watercraft and equipment with high-pressure water, or
  • Rinse with very hot water, or
  • Dry for at least 5 days.

Report New Sightings — note exact location; wrap a plant fragment in a wet paper towel, place in a sealed plastic bag; and call a Minnesota DNR Invasive Species Specialist (see www.mndnr.gov/invasives/contacts.html), 1-888-MINNDNR or (651) 259-5100; or the Minnesota Sea Grant Program in Duluth, (218) 726-8712.

Know the Rules!

Specimens are needed to confirm sightings, but some jurisdictions prohibit possession and transport of invasive aquatic plants and animals. Contact your local natural resource management agency for instructions. Unauthorized introduction of plants, fish, or invertebrates into the wild is illegal. Protect your property and our waters.

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This page last modified on May 04, 2016     © 1996 – 2019 Regents of the University of Minnesota     The University of Minnesota is an equal opportunity educator and employer.
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