Scientific name: Trapa natans

What Is It?

Water chestnut is an aquatic, floating plant, which grows in floating mats and has white or light purple flowers. It grows in lakes, ponds, canals, and other slow-moving water bodies. Dense growth of water chestnut may harm native species and ecosystems, and limit boating, fishing, swimming, and other recreational activities.

Is It Here Yet?

No, it is not yet present in Washington. Water chestnut infests many water bodies on the East Coast.

Why Should I Care?

Water chestnut’s dense mats restrict light, reduce oxygen, and displace other emergent and floating vegetation. It is of limited value to wildfowl. Dense water chestnut growth limits boating, fishing, swimming, and other recreational activities, and the sharp spines on nuts may puncture shoes or hurt bare feet.

How Can We Stop It?

Learn to identify this species and participate in hand removal efforts if populations establish. It is on Washington’s Wetlands and Aquatics Quarantine list, meaning it is prohibited to transport, buy, sell, offer for sale, or distribute water chestnut plants or plant parts.

What Are Its Characteristics?

  • Rooted, floating plant, which forms dense floating mats in slow-moving water 12-15 feet deep
  • Leaves on the water’s surface are alternate, triangular (or diamond-shaped), strongly toothed, and shiny on the upper side.
  • Leaves connect to the limp stem by swollen stalks just below the leaf blades.
  • Submerged leaves may be long, narrow, or feathery, and may be considered roots.
  • White or light purple, four-petaled flowers bloom from mid-summer to frost, then produce nut-like fruits with 2-4 short, barbed spines.

How Do I Distinguish It From Native Species?

This species is not related to the edible Chinese water chestnut.

Additional Photographs