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Noxious weeds

King County, Washington

To offer a suggestion or report an error on the King County Noxious Weeds website, please contact Sasha Shaw, education specialist.

Myriophyllum aquaticum

Parrotfeather stems - click for larger imageThis aquatic plant is a Class B noxious weed in Washington State. Control is required in King County and we are interested in knowing where this plant is growing in the county. Because of its limited distribution in King County, there is an opportunity to stop its spread and work towards eradication.

Parrotfeather has been popular as an ornamental in ponds and aquariums, but because it rapidly takes over lakes, ponds and ditches, this species is on the Washington quarantine list (known as the prohibited plants list) (external link) 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 laws and lists.

Identification (see below for more photos)

Parrotfeather stem by canal - click for larger imageSpikes of feathery leaves emerge up to a foot above the water, looking like miniture pine trees growing on the water's surface. Below the water, the leaves are less stiff and closely resemble other types of milfoil, but the plant is easily distinguished by its stiff, bright green upper stems. The feathery leaves grow in whorls of four to six (meaning that there are four to six "feathers" attached at the same point on the stem that radiate out in a circle around the stem). Parrotfeather on the water - click for larger imageStems are robust, even under water, and roots form along the stem. Flowers are white, tiny and inconspicuous and are found where the above-water leaves attach to the stems. Because all plants in the United States are female, parrotfeather doesn't form seeds but it does spread readily by fragmentation of stems and rhizomes. In King County, parrotfeather emerges in late May and persists into October.

Where it grows

Parrotfeather infestation in a pond - click for larger imageParrotfeather forms dense mats of vegetation and can be found growing along lake and pond edges and slow-moving waterways. Even when attached to the bank, stems can extend several yards out over the water's surface and it has also been found growing as a floating mat in some lakes. It has even been found growing up onto the soil along the edges of ponds. In King County, parrotfeather is mostly found in private ponds. However, in other parts of the state, it is found in drainage canals, lakes, and rivers. For instance, parrotfeather is found throughout the drainage system of the Longview/Kelso area.


Parrotfeather swamping a paddleboat - click for larger imageAlthough parrotfeather is a native of the Amazon River in South America, it has naturalized throughout the world. In Washington State it has become entrenched in several drainage systems and even small infestations are highly challenging to control. Although it doesn't grow in deep water, parrotfeather can completely cover and fill in shallow water. The dense growth causes problems for boating, swimming, fishing or other water recreation. It encourages mosquito growth and can increase flooding. In rivers, it can impact salmon habitat, especially in side channels where juvenile salmon rear.


Controlling parrotfeather with aquatic herbicide - click for larger imageParrotfeather is costly and difficult to remove once it is established in a waterway. We encourage King County property owners to contact our program for assistance controlling this plant.

Small populations can be pulled or raked up, being very careful to remove all fragments from the water. Manual control requires persistence over many years.

Aquatic herbicides can be effective if applied correctly, but can only be applied by a licensed pesticide applicator with an aquatic endorsement and will likely require a permit to use in water.

Additional information on parrotfeather

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

Please notify us if you see parrotfeather 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. Also, because parrotfeather is not established in King County, we have an opportunity to stop it from spreading if we act quickly. We map all known locations of regulated noxious weeds such as parrotfeather in order to help us and others locate new infestations in time to control them.

Parrotfeather photos - click thumbnail for larger image

Parrotfeather drawing - click for larger image Parrotfeather and ludwigia in canal - click for larger image Parrotfeather closeup - click for larger image
Parrotfeather by paddleboat - click for larger image
Parrotfeather stem in hand - click for larger image Parrotfeather growing with ludwigia - click for larger image Parrotfeather infestation on edge of pond - click for larger image


Report parrotfeather in King County, Washington

Locate parrotfeather 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).