Water Caltrop
Exotic Aquatic Invasive Species

The Return of the Non-Native

Water Caltrop (Trapa bicornis),a.k.a. Water chestnut, Buffalo nut, Bat nut, Devil pod, Ling nut, Singhara, or Pani-phal, has claimed the biggest prize in our watershed, Lake Accotink itself.

On a series of October workdays, Park Authority staff and volunteers set out with buckets, bags, rakes, and kayaks to try to put an end to the infestation in Lake Accotink. Patches of this weed were found in the marina, along the face of the dam, all around the perimeter of the lake, and back among the islands. The eradication efforts were diligent, but there can be no certainty that some plants did not escape detection.

Even as the volunteers removed one invasive species, they observed mats of Floating Primrose-willow (Ludwigia peploides), a semi-aquatic invasive species that will be more difficult to address.

Other water bodies, all smaller ponds, which have known infestations in our watershed are at Vienna Metro, Franconia Metro, Brookfield Pond, the Northern Virginia Community College pond, and a stormwater pond in Merrifield owned by Inova. Geese carrying the barbed seedpods on their feathers seem to be the primary vector.

Water caltrop forms thick floating mats that can expand exponentially, shading out native submerged aquatic vegetation, causing declines in dissolved oxygen, and interfering with boating.

USGS map of Trapa bicornis locations Select "Records" tab for text details of locations.
USGS Trapa bicornis description
Fairfax County Water Caltrops page
2019 Water Caltrop Report

Innocent-looking, but sinister Water Caltrop in Lake Accotink marina - Sophia Chapin
See more eradication workday photos