Eurasian watermilfoil

Scientific Name: Myriophyllum spicatum

Alison Fox, University of Florida, Bugwood.orgCopyright Info

Identification: Eurasian watermilfoil is a plant that grows rooted to the bottom. It has long, underwater stems that branch and produce many leaves upon nearing the surface. The leaves are divided into thread-like leaflets, usually in pairs of more than 12 to 14, forming a feathery shape. Leaflets of the uppermost leaves of Eurasian watermilfoil taper to a squarish tipped leaf. This species can be distinguished from native northern watermilfoil (Myriophyllum sibiricum), whose long leaflets occur in fewer than 11 pairs and extend almost to the leaf tip, resulting in rounded uppermost leaves. In addition, northern watermilfoil tends to grow close to the bottom, while Eurasian watermilfoil grows up to the water surface.

Size: Eurasian watermilfoil stems can reach lengths of 33 feet (10 m). Leaves are less than 2 inches (5 cm) long.

Native Range: This plant is native to Europe, Asia, and northern Africa.

Means of Introduction: Eurasian watermilfoil was probably intentionally introduced to the United States, and its dispersal has been linked to the aquarium and nursery trades. In 1942, it was first documented in a Washington, DC pond. Long-distance spread of Eurasian watermilfoil occurred as the species was planted into lakes and streams across the country. While the outward growth of horizontal stems from established plants expands local colonies, stem fragments are important to the colonization of new habitats. Motorboat traffic helps create fragments and distributes them within a lake or river. Transport on boating equipment plays the largest role in introducing fragments to new water bodies.

Status: This species is one of the most widely distributed of all non-native aquatic plants. It has been confirmed in 45 American states and in the Canadian provinces of British Columbia, Ontario, and Quebec. It is present in all of the Great Lakes.

Remarks: Millions of dollars have been spent nationwide on control efforts. Annual costs to control Eurasian watermilfoil are estimated at $500,000 in New York alone. Conventional control efforts, such as application of herbicides and reservoir drainage, have been unsuccessful in providing more than short-term relief.

Since 1963, the grass carp (Ctenopharyngodon idella) has been released to suppress Eurasian watermilfoil and other nuisance aquatic plants in many North American sites. Researchers are looking for additional natural enemies that could be used to control the Eurasian watermilfoil’s growth and spread. The most promising are two insect species: a non-native moth (Acentria ephemerella) and a native weevil (Euhrychiopsis lecontei). The weevil has been shown to heavily feed on Eurasian watermilfoil, causing significant damage, while having little impact on native species.

Other Resources:
GLANSIS Technical Species Profile

Eurasian Watermilfoil (WA Department of Ecology)

Author: Illinois-Indiana Sea Grant

Contributing Agencies:
NOAA Sea Grant GLRI Logo

Revision Date: 9/25/2012

Citation for this information:
Illinois-Indiana Sea Grant, 2018, Eurasian watermilfoil: U.S. Geological Survey, Nonindigenous Aquatic Species Database, Gainesville, FL, and NOAA Great Lakes Aquatic Nonindigenous Species Information System, Ann Arbor, MI,, Revision Date: 9/25/2012, Access Date: 3/24/2018

This information is preliminary or provisional and is subject to revision. It is being provided to meet the need for timely best science. The information has not received final approval by the U.S. Geological Survey (USGS) and is provided on the condition that neither the USGS nor the U.S. Government shall be held liable for any damages resulting from the authorized or unauthorized use of the information.