This noxious weed is a submersed, freshwater perennial plant found in both still and flowing waters including lakes, ponds and quiet streams. Brazilian elodea tends to form dense monospecific stands that can cover hundreds of acres.

Native to Brazil and Argentina, Brazilian elodea is a popular aquarium plant often sold in pet stores and available in school science kits under the name Anacharis. When it is introduced into freshwater, it forms dense beds that reduce water quality and impede recreational activities. It is illegal to sell this plant in Washington State.

This aggressive aquatic plant has spread into many western Washington lakes including Lakes Washington, Union, Sammamish, Fenwick, and Doloff in King County. State officials in Oregon consider Brazilian elodea to be their worst aquatic plant problem but in Washington there is still a chance to contain it. In King County, most small lakes and waterways are still free of this weed, so there is still a chance to keep this aquatic pest from impacting most of King County.

Identifying Brazilian elodea (Egeria densa) can be tricky so be sure to get an expert to confirm the species before planning any control measures. The plant grows mostly underwater but can form dense mats along the surface. Leaves grow in whorls around the stem making a cylindrical shape and the stems are very leafy compared to the native elodea, common waterweed (Elodea canadensis). Brazilian elodea plants usually have 4 to 8 leaves in a whorl and the leaf edges appear smooth to the naked eye (native elodea has 3 leaves in a whorl). Small white flowers appear from spring to late summer. They have three petals and float on or rise above the water's surface on thread-like stems.

Legal status in King County, Washington

Public and private landowners are required to control infestations of Brazilian elodea that occur on their property in King County, Washington except in lakes Dolloff, Fenwick, Union, Washington, and Sammamish, and the Sammamish River. Brazilian elodea is a Class B Noxious Weed in Washington, first listed in 1993. It is designated by the Washington State Noxious Weed Control Board for required control in King County except in areas as described above. It is on the list of Regulated Class B Noxious Weeds in King County.

This species is also on the Washington quarantine list (known as the prohibited plants list) and it is prohibited to transport, buy, sell, offer for sale, or to distribute plants or plant parts of this species, into or within the state of Washington. It is further prohibited to intentionally transplant wild plants and/or plant parts of this species within the state of Washington.

For more information on noxious weed regulations and definitions, see Noxious Weed Lists and Laws.

Additional information on Brazilian elodea

• King County Best Management Practices for Brazilian Elodea
• Washington State Noxious Weed Control Board (external link)

What to do if you find this plant in King County, Washington

Please notify us if you see Brazilian elodea growing in King County. Our program staff can provide the property owner or appropriate public agency with site-specific advice on how best to remove it.  We map all known locations of regulated noxious weeds such as Brazilian elodea in order to help us and others locate new infestations in time to control them.

Brazilian elodea photos

Report Brazilian elodea in King County, Washington

• Please notify us through our online infestation form

Locate Brazilian elodea in King County, Washington

• Use our interactive noxious weed map and search for Brazilian elodea

Related information

• Lakes
• Northwest yard and garden
• Animals, plants and habitat
• Wetland topics

Related agencies

• Dept. of Natural Resources and Parks
• Water and Land Resources Division

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Program offices are located at 201 S. Jackson St., Suite 600, Seattle, WA 98104. To contact staff, see the Noxious Weed Control Program Directory, send an email, or call 206-477-WEED (206-477-9333).