Aquatic Invasive Species

Water Chestnut Eradication Report

1999-2017

Water chestnut was first recorded in North America near Concord, Massachusetts in 1859. Since that time, wild populations have become established in many locations in the Northeastern United States. Water chestnut was recorded for the first time in the Bird River in Baltimore County in 1955. The Maryland Departments of Game and Inland Fish and Tidewater Fisheries used mechanical removal and chemicals (the herbicide 2,4-D) to control the population.

In 1964, water chestnut reappeared in the Bird River and an additional 100 acres were discovered in the Sassafras River in Kent County. Thirty acres were mechanically removed from the Sassafras River in 1964. A combination of removal techniques were used once again in 1965, when 200 acres were eradicated on the Sassafras.

The harvesting efforts were believed to have been successful, and no plants had been reported until the summer of 1997 when a landowner on the Bird River noticed an unusual plant. This led to the discovery of a small population of water chestnut in a cove just upriver from Railroad Creek. From the summer of 1997 to the summer of 1998, these plants expanded from 3 acres to approximately 30 acres, and reports were also received of water chestnut growing in Lloyds Creek of the Sassafras River. Both populations were in the same locations from which water chestnut had been harvested in the 1960's, suggesting that this was a resurgence of the same population of plants.

The Maryland Department of Natural Resources has been attempting to eradicate water chestnut from the Bird River, Harford County and the Sassafras River, Kent County since 1999. The population in the Bird River had spread from approximately 50 plants in the summer of 1997 (based on conversations with local landowners) to over three acres in 1998. By this time, the three-acre area was so heavily covered with plants that the water beneath the plants was barely visible. The Sassafras population was believed to be slightly larger, but determining the exact quantity was not possible.

Based on conversations with aquatic plant control experts from around the country, it was decided that application of the herbicide 2,4-D would be a safe and effective control technique. Despite this advice, public and state concern over the application of an herbicide to Chesapeake Bay waters lead the department to save herbicide application as a last resort in the event that other techniques didn’t work. It was decided to launch a large mechanical and hand removal effort. This effort has been ongoing since 1999. This control has prevented water chestnut from becoming a nuisance to water contact recreation, but total eradication has not been possible. Below are brief annual summaries of efforts to date.

Water Chestnut Management Timeline

Water Chestnut annual harvest graph.

* In 1999, the harvest on the Bird was 140,000, 260,000 on the Sassafras. In 2000, 1000 bushels were harvested on each river.

1999

  • Mechanical harvesting using an aquatic plant harvesting boat took place in June on the Sassafras and the Bird, removing an estimated 260,000 pounds of water chestnut.

  • A person on a harvesting machine in the water.

  • A follow-up hand harvesting effort took place in July to clean up the remaining plants.
  • All harvested plants were composted in the water using floating cages designed specifically for the project.
  •  A biologist stainding on harvested plants that were composted in the water using floating cages.

2000

  • A combination approach was used, with mechanical harvesting by boat followed by hand removal by volunteers. Approximately 30 volunteers manually removed plants from the Sassafras River and 40 volunteers manually removed plants from the Bird River.
  • Less than 1000 pounds of plants were discovered and removed from rivers in 2000, indicating that mechanical and hand removal efforts were successfully reducing the population.

2001

  • In the Sassafras River, about 2 acres of Lloyds Creek and 3 acres of Shallcross Creek contained scattered plants. The harvester cut and collected the majority of plants over the course of two days. Groups of volunteers searched for additional plants in late June removed several more bushels.
  • In the Bird River, the harvesting boat was operated for one day, cutting less than 150 pounds of plants from a small tributary upriver of Railroad Creek. Volunteers finished the job on June 15th, with only a handful of additional plants being collected.

2002

  • Efforts once again took place on both the Bird and the Sassafras River in mid to late June, using approximately 80 volunteers. The total volume of plants harvested declined once again, with only a few bushels of plants harvested from the Bird River, and about 200 pounds of plants from the Sassafras. The combination of mechanical and hand removal of plants from 1999-2002 has proven to be so successful that there had been no need to resort to herbicides to control this pest.
  • Not enough plants were present at any of these locations to justify using a mechanical harvester- a significant milestone for the overall eradication effort.

2003 - 2006

  • Beginning mid-June, department personnel surveyed all shoreline areas in the vicinity of the original populations and for several miles along the shoreline both upriver and downriver. In each year, a few hundred plants were found in each river in generally the same areas as the first several years. Control efforts were performed on both rivers each year using personal watercraft, department work boats, canoes and kayaks.
  • In 2004, a substantial additional population of plants was discovered in a small pond off the eastern shore of Woodland Creek not easily visible from the river. Approximately 600 pounds of water chestnut were harvested from this pond and the cove into which it outflows. In 2005, no plants were found in this pond.

2007

  • The Sassafras River Association joined the effort to control water chestnut, and assisted with the collection in June.
  • A private landowner off of Woodland Creek contacted the department to request a biologist survey his sediment pond. Approximately 2 acres of the pond were covered with water chestnut. After an unsuccessful hand removal effort, the pond level was lowered significantly over the winter in an attempt to kill the seeds by freezing.

2008

  • The pond discovered in 2007 was treated in July with Clearcast (an aquatic herbicide). This was effective, and little water chestnut left in the pond in the summer of 2009. An outreach effort was conducted though the Sassafras River Association to find any private landowners that may have water chestnut infestations on their property, but no other infestations were reported.
  • On the Bird river, approximately 25 bushels of plants were removed by hand from a small, unnamed creek adjacent to Railroad Creek and Taylor Creek (adjacent to Mariner Point Park).
  • Department biologists worked with the Sassafras Riverkeeper and volunteers from the Sassafras River Association to remove 60 bushels of water chestnut from Turners Creek, Dyer Creek, Woodland Creek, Island Creek and a small cove behind Pond’s Bar adjacent to the Sassafras Natural Resources Management Area. The majority of the plants were collected from Turners Creek.

2009

  • A record low two bushels were harvested on the Sassafras River, with most of them found in Lloyds and Woodland Creeks.
  • On the Bird River, 10 bushels were harvested in Days Cove. Plants were found in the same general areas as previous years.

2010

  • After a year of record lows on both rivers, it became obvious the seed bank that repopulates these areas is fairly substantial.
  • On the Sassafras River, a sharp increase in population was observed, with 220 bushels being collected in Lloyds Creek and 120 bushels collected in Turners Creek.
  • On the Bird River, 25 bushels were found in Days Cove.

2011

• 50 bushels were collected on the Sassafras River and 40 bushels on the Bird River.

2012

  • The Sassafras River had a sharp decrease in water chestnut in Lloyds and Turners Creek, but an increase in Woodland, Island and Dyer Creeks. Crews from the department and the Sassafras Riverkeeper removed 30 bushels in the Sassafras, but were forced to cut the harvest short due to Mycrocystis blooms starting in June.
  • On the Bird River, department field staff and interns removed 12 bushels.

2013-2016

  • From 2013 to 2016, the populations of water chestnut on both rivers remained relatively constant, usually yielding about 25 bushels each year. Without a dedicated funding stream, the department continues to partner with the Sassafras Riverkeeper and volunteers to assist the field staff with removal efforts.
  • In late summer 2016, the Sassafras Riverkeeper reported an expansive infestation in the upper reaches of Lloyds Creek. Unfortunately, most of the seed pods had already dropped, so it was decided a larger effort would be put into Lloyds Creek in 2017.

2017

  • In 2017, the Sassafras Riverkeeper organized thirty-eight volunteers - as diverse as local citizens, residents of Easton and Gaithersburg, the Maryland Department of Natural Resources, and three groups from AmeriCorps, to paddle kayaks and canoes to help clear harmful water chestnuts from our tributaries. Department field staff joined the volunteers to provide assistance with three state vessels to remove the plant material. Over 85 bushels of invasive water chestnut plants were collected from Dyer Creek, Turners Creek, and Lloyd’s Creek.
  • Due to depth limitations, boats can only access this area of the creek at high tide. More than 100 man hours were devoted to this infestation, but not all plants were removed. The increase in abundance and distribution of American lotus (Nelumbo lutea) has made water chestnut control more and more difficult in the Sassafras River. The two species overlap in distribution, and water chestnut plants can be difficult to see in dense lotus beds (picture). The department may attempt to harvest after the lotus dies back in the fall.
  • On the Bird River, less than two bushels of water chestnut were collected. department staff used kayaks to conduct a broad search between Mariner Point and Days Cove. GPS points were marked and year to year, small groups of plants are found in the same general areas where water chestnut was first discovered.
Figure 1. Water chestnut infestation in the headwaters of Lloyds Creek. Figure 2. Department biologist collects water chestnut in Turners Creek.

Figure 3. Bird river water chestnut locations. Historic coverage is in red, 2017 distribution in green.


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Figure 4. Sassafras River water chestnut locations. Historic coverage is in red, 2017 infestations are in green. Individual creeks where water chestnut was found in 2017 are below.


 

Figure 5. Lloyds Creek, Sassafras River


 

Figure 6. Shallcross Creek, Sassafras River


 

Figure 7. Turners Creek, Sassafras River