Brazilian elodea
Egeria densa

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, the only large infestations are in Lake Washington and Lake Fenwick, so there is still a chance to keep this aquatic pest out of the many other lakes and waterways of the county.

Identifying Brazilian elodea 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). There are usually 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

Brazilian elodea is a Class B Noxious Weed in Washington State. In King County, control is required everywhere except Lakes Union, Washington, Sammamish and Fenwick.

Additional information on brazilian elodea

• Washington State Noxious Weed Control Board (external link)
• King County Best Management Practices for Brazilian Elodea
• Technical Information Bulletin from the WA State Department of Ecology

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 - click thumbnail to see larger image