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Trapa natans

LHPrism Status 
Tier 4 - Widespread
Species Type 
  • Aquatic Invasives
  • Plants
Lake or Pond
Impacts of this species 

Trapa natans form in large mats along the surface of water. These mats cause significant competition against native plants for space and for available nutrients. For animals that favor and ingest these plants, they are provided with a severe lack of nutritional value and may be detrimental to their health. Lower levels of dissolved oxygen in the water systems may occur in response to the water chestut decomposing after blooming. This encourages algae blooms and eutrophication of lakes. The spiny fruits produced by these plants can cause health risks to domesticated animals by possible foundering dogs and horses. The extensive spread of water chestnut can also reduce recreational value of streams and lakes by impeding fishing, hunting, swimming and boating.


Trapa natans is native to warm temperate regions of Europe, Asia and parts of Africa. It was first introduced to North America in the mid-1800's. The plant was figured to have escaped local cultivation and was found growing in the Charles River in 1879. Later, in the 1880's, it was intentionally introduced to New York lakes for waterfowl food. The water chestnut quickly became widespread, and in New York state has been prohibited against sale, importation, purchase, transportation or introduction.

The water chestnut is an annual aquatic plant that has a submerged flexous stem that anchors itself into mud and extends itself upwards towards the water surface. It has a rosette of floating, fan-shaped leaves. Each of the leaves have an inflated petiole and dentate leaf margins. From the center of the rosette forms solitary, small, white flowers that have four petals. These flowers are in bloom usually from July until the plants are killed by frost. Four, orthogonal, sharp spines develop from hardened sepals can be seen on their large fruits.

Trapa natans is established throughout many New England states and is widespread in the Lower Hudson region. This plant is most prominent in shallow waters, although it can be found in waters up to 12 ft. in depth. The water chestnut can also be found in freshwater regions of estuaries and mudflats. They thrive in nutrient-rich lakes as well as slow-moving streams and rivers. While they can survive in a range of water conditions, they thrive best in water with a pH of 6.7-8.2 and is slightly alkaline.  

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