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Egeria (Brazilian elodea) identification and control: Egeria densa

Egeria (Brazilian elodea) identification and control

Egeria densa


Egeria, also known as Brazilian elodea or Egeria densa, is a submerged freshwater perennial plant that forms dense stands in still and flowing waters up to 20 feet deep. It can also create dense, floating mats along the water's surface. Apparently smooth-edged leaves grow in whorls, making a cylindrical shape, with 4-7 leaves per whorl. Spring to late summer, the plant produce small, white, 3-petaled flowers that float on or rise above the water's surface on thread-like stems. Identifying egeria can be tricky, so be sure to get an expert to confirm the species before planning any control measures.


Egeria might be confused with a native water plant called elodea or common waterweed (Elodea canadensis). However, Egeria's stems look very leafy compared to those of the native elodea, and the native elodea has only 3 leaves in a whorl, instead of 4-8 like egeria.

Distribution and Impacts

Brazilian elodea in hand

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

Brazilian elodea in Lake Doloff

Native to Brazil and Argentina, egeria 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.

Brazilian elodea in Lake Fenwick - click for larger image

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 egeria 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.

Brazilian elodea flowering
Brazilian elodea closeup

Legal status in King County, Washington

Public and private landowners are required to control infestations of egeria that occur on their property in King County, Washington except in lakes Dolloff, Fenwick, Union, Washington, and Sammamish, and the Sammamish River. Egeria (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.

Egeria 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 egeria

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

Please notify us if you see egeria 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 egeria in order to help us and others locate new infestations in time to control them.

Egeria photos

Diver with Brazilian elodea in Lake Union
Handful of Brazilian elodea in Thurston County
Brazilian elodea on boat motor
Dense patch of Brazilian elodea in Thurston County
Dense infestation of Brazilian elodea in Thurston County

Report egeria in King County, Washington

Locate egeria in King County, Washington

Related information

Related agencies

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).