Water Chestnut

On this page:

• New York locations
• Identification
• How it spreads
• Environmental impact
• Management
• Best management practices for removal projects

Water chestnut is an aquatic invasive plant that is native to Eurasia and Africa. It was introduced in the United States in the mid-1800s as an ornamental plant. Water chestnut colonizes shallow areas of freshwater lakes and ponds and slow-moving streams and rivers and negatively impacts aquatic ecosystems and water recreation.

Description

Water chestnut is an annual plant that has:

• Hollow, air-filled stems 12-15 feet long that has fine roots that anchor it to the soil triangular floating leaves with saw-toothed edges that form a rosette around a central point.
• Tiny, white four-petaled flowers that bloom in June. Each rosette can produce up to 20 hard seeds.
• Seed that are four-inches long and have barbs along them. Seeds within fruits can remain viable for up to 12 years.

Water chestnut fact sheet (PDF)

Distribution

Water chestnut has been found in more than 40 counties in New York State. For a map of where water chestnut has been documents, please visit iMapInvasives' interactive mapper (leaves DEC website).

Spread

Water chestnut spreads by rosette and fruits detaching from the stem and floating to another area. They also spread by clinging to floating objects including recreational watercraft, the pads of boat trailers, and fishing equipment.

Environmental Impact

Water chestnuts form dense mats of rooted vegetation that can be very difficult to get through in a boat, kayak, canoe, or when swimming. Water chestnut fruits are often found along the shoreline and bottom of waterways - they have very sharp spines with barbs that can cause painful wounds when stepped on. The dense mats of vegetation shade out native aquatic plants that provide food and shelter to native fish, waterfowl, and insects. Decomposition of these dense mats reduces dissolved oxygen levels and may kill fish. Property values along shorelines of infested waters may also decrease.

Management

Water chestnut can be controlled using manual, mechanical, and chemical methods. As with all other infestations, early detection is key for containing and controlling spread. DEC is currently funding research on biocontrol - a study of the effectiveness of predator insects from water chestnut's native range - in controlling the spread of water chestnut.

The smaller the size of the infestation, the more easily it can be eradicated, and its economic and ecological impacts reduced. Because water chestnut is an annual plant, effective control can be achieved if seed formation is prevented.

A site may be a candidate for eradication (eliminating the plant from the area entirely) if:

• small in size (trace-sparse density),
• detected and treated early (no significant seed bank has been established),
• located within an isolated body of water, or is an isolated population within a larger body of water (unlikely to be re-infested),
• clean, drain, dry participation prevents new introductions,
• there is safe access for manual (hand-removal) efforts.

A site may be a candidate for suppression and containment (reducing the size of the patch or preventing it from spreading) if:

• medium in size (sparse-medium density),
• a long-term commitment to management/monitoring as seeds in the seed bank may be viable for up to 12 years,
• clean, drain, dry participating prevents new introductions,
• strategic removal of portions of the infestation would protect high quality native plant beds or other important features.

A site may be a candidate for maintaining access (preventing the patch from obstructing use) if:

• large in size (medium-dense density),
• population (and seed bank) has been established for many years,
• repeated introductions are likely from other nearby infestations due to tides/streamflow/motorboat transport, etc.,
• adjacent to boat ramps, docks, swimming beaches, or sampling sites where need for access makes continued maintenance necessary.

Best Management Practices for Removal Projects

Hand-pulling/Manual Removal

• Hand-pull rosettes when they first appear (mid-June to early July), before seeds are developed.
• Remove as much of each plant as possible, including the stems, any developing seeds, and roots.
• Avoid pulling native aquatic plant species, if possible.
• Identify access areas, disposal site, and location for storing harvested plants during the drying process.
• Start at the edge of the infestation and work towards the center.
• If possible, revisit the site repeatedly to pull plants that continue to sprout throughout the growing season.
• Repeat plant removal early each growing season until the seed bank has been depleted.
• Monitor site for a minimum of 12 years to ensure seed bank has been depleted and no new introductions have occurred from other sources.

Mechanical Removal/Machine Harvesting

• Conduct an aquatic plant survey to determine whether harvesting would also eliminate native and/or protected species.
• Identify access areas, disposal site, and location for storing harvested plants during the drying process.
• Harvesting machines can be used when rosettes first appear (mid-June to early July) before seeds are developed.
• Remove as much of each plant as possible, including the stems, any developing seeds, and roots.
• Repeat plant removal early each growing season until the seed bank has been depleted.
• Monitor site for a minimum of 12 years to ensure seed bank has been depleted and no new introductions have occurred from other sources.
• Avoid mechanical harvesting if water chestnut is accompanies by other invasive species that reproduce via fragmentation such as Eurasian watermifoil (leaves DEC website).

Chemical/Herbicide Control

• Aquatic herbicides approved for use in New York can be effective including florpyrauxifen-benzyl, imazamox, 2, 4-D, and glyphosate.
• Herbicides must be applied by a licensed applicator according to label requirements and any necessary permit requirements.
• Conduct an aquatic plant survey to determine whether products would also impact native and/or protected species.
• Identify boundaries for the treatment area and determine any risks to non-target species.
• Repeat herbicide treatment or combine with manual and/or mechanical control methods until seed bank has been depleted.
• Monitor site for a minimum of 12 years to ensure seed bank has been depleted and no new introductions have occurred from other sources.

Disposal

• For small infestations, plants can be places in black trash bags and left in the sun before placing in trash; or
• dispose of plants in compost, far away from water sources, or allow to dry in piles far from water and then incinerate.
• Larger infestations will require careful coordination with local municipalities to transport plants/seeds away from water sources and compost them on land without risk of spreading the plants.

How You Can Help

• Clean, drain, and dry your watercraft and equipment thoroughly before visiting other waterbodies. 
• • Inspect and remove debris and mud from boats, trailers, and equipment. 
  • Dispose of all debris and bait in trash cans or at disposal stations. 
  • Drain all water-holding compartments including live wells, bait wells, and bilge areas. If possible, visit a decontamination station and disinfect compartments with hot water (140°F) for at least 30 seconds. 
  • Dry boats, trailers, and all equipment before use in another water body. A minimum of 5-7 days of drying time in dry, warm conditions is recommended. 
• Do not dump aquarium contents in any waterbodies, drainage ditches, or sewers. 
• Learn how to identify water chestnut and report any encounters.

Early detection of infestations helps to reduce removal costs and ecological impacts. If you think you've found water chestnut:

• Email the photos, noting where it was caught (coordinates preferred), to isinfo@dec.ny.gov, OR 
• Submit a report through iMapInvasives (leaves DEC website), OR 
• Contact your local Partnership for Regional Invasive Species Management.