Volunteers Community Partners

Water Chestnut Control

Water Chestnut Control Project
Funded by: Environmental Protection Agency- Great Lakes Restoration Initiative, $516,367.00
Years: 2016-2018
Project Manager: Kate Des Jardin, desjardin@hws.edu

Impenetrable mats of water chestnut can cover large expanses of water, altering water quality and clarity, eliminating the growth of native aquatic plants, and making boating, fishing, and swimming hazardous. Photo by Leslie J. Mehrhoff, University of Connecticut, Bugwood.orgWater chestnut (Trapa natans) is a highly successful invasive species from Eurasia that has invaded waterbodies in multiple locations across the Finger Lakes region in the watershed of the Great Lakes basin. Floating rosettes of leaves form dense mats that shade the water column, which negatively affects the aquatic community and inhibit recreational activities and boat navigation in area waterways. In order for control efforts to succeed, the seeds must be chemically treated or removed before they mature and drop in a given year, since water chestnut is an annual plant. This reduces the population potential in subsequent years given the exponential growth rate for the plant. Unfortunately, seeds from long‐standing infestations have the potential to remain viable for up to 10 years.


In 2016, the Finger Lakes Institute (FLI) at Hobart and William Smith Colleges (HWS) was awarded an Environmental Protection Agency’s Great Lakes Restoration Initiative (EPA GLRI) grant to survey and control for known water chestnut infestations and provide early detection and rapid response to other high risk invasive species in the Finger Lakes region. This involved organizing a strike team and working with partners and stakeholders to manage 43 acres of water chestnut across 12 sites. Sites for control Flowers with four white petals normally bloom in July. Photo by Leslie J. Mehrhoff, University of Connecticut, Bugwood.orgwere pre-selected from areas of ecological importance, including Areas of Concern (AOC’s), Important Bird Areas (IBA’s), and Significant Natural Communities. Additional sites were surveyed and controlled as capacity allowed. Various methods, including physical, mechanical, and chemical control, were employed to manage water chestnut at project sites.

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Year Project Target (acres) Number of Sites Survey Area (acres) Managed (acres) Biomass Removed (lbs wet weight) Days on Site Volunteer Person-hours Notes


16 9,679 179 72,314 48.5 1,060 Biomass removed included harvested weights
2017 18 3,198 775 29,264 40 1,210 Biomass removed included only hand-pulled material
2018 21 3,769 1,540 41,185 38.5 404.5 Biomass removed included only hand-pulled material

Additional partner efforts totaled over 200 person-hours of field work

Total 16,646 2,494 142,763 127 2,675


Throughout the three project years, over 147,000 students, homeowners, boat slip users, recreationists, and community members were engaged at trainings, presentations, and events regarding the identification of and negative impacts caused by water chestnut and other aquatic invasive species, including the NYS Fair, National Hunting and Fishing Days, and Conservation Field Days.

An invasive species field guide and fact sheets were created and disseminated across the Finger Lakes region. These contain profiles and distribution maps of high priority invasive species that may be found in or near aquatic habitats and are intended to aid members of the public in the identification and management of invasive species. Electronic versions of these documents are located here:

A macrophyte survey program was developed to engage the community to enable rapid discovery and response to a localized infestation of water chestnut and other high priority invasive species. Participants learned to survey for, identify, and report three high priority species: water chestnut, Hydrilla (Hydrilla verticillata), and starry stonewort (Nitellopsis obtusa). This program began in its pilot form in 2017.

Seven lake associations and eleven volunteers participated in the macrophyte survey program, which included an initial training on macrophyte identification and data collection. Participants conducted rake tosses four times per month for three months of the growing season in Canandaigua, Cayuga, Conesus, Honeoye, Keuka, Skaneateles, and Owasco Lakes. There was a total of 123 rake tosses for the season.

In 2018, 24 volunteers across eight lakes participated in the macrophyte survey program. Rake tosses were conducted bi-weekly for five months of the growing season across Cayuga, Conesus, Hemlock, Honeoye, Loon, Cayuta, Lamoka, and Waneta Lakes, for a total of 211 rake tosses. Throughout the two seasons, none of the three high priority invasive species were reported.