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Water chestnut 

Water Chestnut Control: Start Early and Continue

by New York Sea Grant Launch Steward Nick Spera

Plants are good for the environment, right? Not always.

Aquatic invasive species (AIS) in local watersheds and ecosystems are negatively impacting native plants, animals, and habitat. An invasive species is defined by the federal Executive Order No. 13112, which establishes a National Invasives Species Council, as a species that is non-native to the ecosystem of interest and whose introduction causes or is likely to cause economic or environment harm or harm to human health.

Locally, European water chestnut (WC), scientifically known as Trapa Natans, is an AIS causing problems in Oneida Lake, the Salmon and Oswego Rivers, and some embayments of Lake Ontario.

Originating from Europe, Asia and Africa, WC has made its way to North America over the years and nows grows, and often thrives, in freshwater habitats such as nutrient-rich lakes and slow moving or stagnant rivers.

Without control efforts, WC plants form dense floating mats that severely limit light and oxygen availability for native species. WC easily outcompetes native species by overcrowding to dominate waterways and increase the potential for fish die-off. Large colonies of WC also negatively affect boating, fishing, swimming and other aquatic recreation.

With such a quickly-reproducing species, control methods can be quite difficult. If not kept in check, WC will flourish and thrive until it clogs one area and begins to spread to surrounding waterways.

How do we manage something that has the ability to spread so rapidly? The answer is through concern, persistence, and dedication. With the help of environmental professionals, communities and volunteers come together to raise public awareness of AIS and take on the challenge of AIS management.

Management and control methods vary depending on the location, level of invasiveness, AIS population size, and local conditions, such as the size of the water body and surrounding ecosystem.

Oswego County Soil and Water Conservation District Manager John DeHollander says the goal of treatment depends on the site characteristics and density of the WC population.

Water chestnut hand pull volunteer
with baskets of WC removed from
lake environment; photo: NYSG/Nick Spera

Hand pulls are done with groups of volunteers, with the goal of removing as much of the WC as possible. Still, some plants can be left behind.  Therefore, it is more reasonable to maintain control over a smaller infested area to prevent the WC from spreading further.

When conditions of a WC infestation are not conducive for a hand pull, other alternatives such as mechanical and/or chemical treatment may be considered.

Mechanical harvesting machines cut and collect the aquatic plants, removing them from the water by a conveyor belt system. The plant matter is then stored in the harvester until the AIS can be removed and disposed away from water. This method works well on large communities of WC that have spread beyond control for mechanical harvesting.

"Speaking from years of experience with mechanical harvesting at the same site (Ox Creek) annually for four years, then skipping the fifth year, we saw the water chestnut move right back in, making it look like the site had never been treated,” DeHollander says.

Eradication is very rare, but may be possible if the WC population is small; however, it would be necessary to continue treatment efforts for several years.

Suppression and containment are more reasonable goals for AIS treatment, particularly for larger AIS populations in isolated ecosystems.

With WC being such a rapidly spreading plant, it is sometimes necessary to control the spread of this AIS using chemical treatment. This sort of “shock” method is used to stop the growth and spread of the AIS so it hopefully becomes possible to regain control of the spread. It is important for local efforts to identify WC invasion early, so control efforts can be made early to prevent having to chemically treat the invasive spread and risk damaging other species in the surrounding ecosystem.

To learn more about organizing a local resource, please reference the "Steps and Procedures to Help Organize an Invasive Plant Removal and Disposal" online at under Fact Sheets at www.nyseagrant.org/ccdstewards.

New York Sea Grant is working with the Oswego County Soil & Water Conservation District (OCSWCD) and St. Lawrence-Eastern Lake Ontario Partnership for Regional Invasive Species Management (SLELO PRISM) to help stop the spread of aquatic invasive species. Volunteers are needed to help control WC where the Salmon River meets Lake Ontario. A pull will be held Saturday, July 13, 8:30am-12:00pm, at Pine Grove State Boat Launch, 7101 State Route 3 at Port Ontario. Volunteers need to bring their own personal floatation device and boat (kayak or canoe works well).

For more information on protecting native habitats against invasive threats, contact New York Sea Grant at 315-312-3042, SGOswego@cornell.edu.

To learn more about how boaters can help slow the spread of AIS, visit the NYSG Launch Steward Program Blog


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