Water Chestnut - Trapa natans

The water chestnut originates from Eurasia and was first brought to the United States in the 1800s. Water chestnuts begin to flower in mid to late July, with their nuts ripening approximately one month later. Flowering and seed production continue into the fall when frost kills the floating rosettes. The mature nuts sink to the bottom when dropped and may be able to produce new plants for up to 12 years. Note: the seed might be edible but is unrelated to the edible water chestnut (Eleocharis dulcis) familiar from Chinese cooking.

See OARS' "Water Chestnut Management Guidance & Five-Year Management Plan for the Sudbury, Assabet, and Concord River Watershed" on our Water Chestnut Management page.


  • Floating leaves form a distinctive rosette
  • Leaves have shiny upperside and fine hairs on the underside
  • Submerged leaves are feather-like and whorled around the stem
  • Four-barbed, one inch fruit may be attached

Water chestnut underside, showing green fruit

Because water chestnut is an annual plant and regenerates from seed, physical removal of the plants before the seed drops each year is an effective control measure. Small patches can be pulled by hand, but larger infestations like on the Sudbury River need to be harvested mechanically. Removal needs to be repeated annually until the patch is under control, because seeds are viable in the sediments for up to 12 years.

You can help!
Help us track water chestnut: print our ID and Reporting Card and take it with you. Mail it back or report via email.

Pull them out: If there are just a few water chestnut plants and you have room in your boat you can pull them out. Caution: this only works for water chestnut! Other species require other types of management. If there are more than a few plants contact OARS and/or your local Conservation Commission to ensure that you are complying with local and state wetland protection regulations when working in the river area.

Volunteer: Or, better yet, volunteer for one of OARS’ water chestnut pulling days in the summer when we attack those larger patches with plenty of help. Watch our Events page for more information in the summer or join OARS, so that you’re among the first to hear about our events.

SOP for Hand-Pulling Water Chestnut

  1. Work safely! Wear a life jacket when boating, work with a partner, and wear gloves (the nuts are sharp).
  2. Pull before mid-August when the plants drop their seeds for the year.
  3. Identify the water chestnuts and note their location.
  4. Pull the entire plant gently out gripping as far down the stem as you can conveniently reach. They are not deeply rooted and should come up easily. Make sure that you get the entire rosette with the nuts (seeds), since the water chestnut spread by seed and as much of the stem as you can (break off the stem if needed).
  5. Put them in a bag or directly in your canoe.
  6. Compost the plants well away from the river so that seeds are not washed back into the river.

(Download a printable version of the directions.)

References and links
Bugwood Archives
Center for Invasive Species and Ecosystem Health