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Top 6 Invasive Aquatic Plants in New England

March 28th, 2018 by Bob Hartzel

New England’s lakes and ponds host a great variety of native plants that are an important part of a healthy aquatic ecosystem.  Non-native species can disrupt these ecosystems by spreading aggressively and displacing beneficial native species.  These plants can also impair swimming, boating, and fishing, and can contribute to water quality problems as large amounts of organic matter decay at the end of each growing season. 

The guide below summarizes the key identifying features of the six non-native plants most commonly found in New England lakes and ponds.


variable milfoil (Myriophyllum heterophyllum)

Variable watermilfoil is a submerged aquatic plant that grows in depths of up to 15 feet. This plant has reddish stems with whorls of 4-6 feather-like leaves that are about 2 inches long and 1 inch wide. As shown in the photo, the plant also produces a prominent spike-like flower (3-6 inches long) that emerges above the water surface by late June or July.



Eurasian milfoil (Myriophyllum spicatum)

Eurasian milfoil has stems that vary from green to red, with 3-6 leaves found in whorls around the stem.  Its feather-like leaves (up to 2 inches long) can be distinguished from other milfoil species by their blunt-ended tips, which look like they have been cut straight across with scissors.  The leaves have 12 or more pairs of thread-like leaflets.  The plants are typically more reddish at the tip.



fanwort (Cabomba caroliniana)

Fanwort is often found growing in shallow water, and can be identified by its bright green, fan-like leaves that emerge from the reddish stem in pairs.  Fanwort has small white flowers that appear at the water surface in late summer.




water chestnut (Trapa natans)

This annual plant can spread prolifically by seed and has the potential to spread aggressively once introduced to a waterbody. Water chestnut can be identified by its “rosette” of serrated floating leaves. If pulled carefully from the sediment without breaking the stem, a spiny nut (see lower photo) can often be found at the base of the plant.






European Naiad (Najas minor)

This invasive plant often has a bushy appearance due to stems that branch profusely at the top. It can be distinguished from other Najas species by its narrow leaves that come to a sharp tip and have 6 to 15 conspicuous teeth (serrations). Other similar-looking naiads have smooth leaves without serrations.





curly-leaved pondweed (Potamogeton crispus)

Curly-leaved pondweed can be identified by the wavy appearance of its finely-toothed leaves (up to 3 inches long). In New England, this invasive plant often reaches its peak of growth in late spring or early summer, then dies back during the summer months. 




















 For more information on invasive species or other lake management issues, contact Bob Hartzel, Certified Lake Manager, at (508) 281-5201 or rhartzel@ceiengineers.com

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