Eurasian Watermilfoil

Myriophyllum spicatum

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Eurasian Watermilfoil- a fully submerged escaped ornamental perennial that readily alters aquatic ecosystems by multiplying quickly and blocking sun with dense "floating" mats.

Leaves: Feather-like leaves occur in whorls of 4 on a red stem. Each leaf can have 12+ leaflet pairs.

Flowers: Tiny pink-reddish flowers appear as terminal spikes. Male and female flowers appear on the same plant.

Habitat: Highly adaptable to any freshwater body including streams, rivers, ponds, lakes and ditches. Has been found as deep as 10 meters.

Classification: B Select

This aquatic weed is confirmed to be present in Carlisle lake, Riffe & Mayfield lakes (and the downstream portions of the Cowlitz), and Mineral lake. It has been nearly eradicated in Mineral lake since being treated last year (2021). Mineral lake's success is in part due to its early detection in the waterbody. Within the Cowlitz river basin, Eurasian Watermilfoil is managed by treating during regularly scheduled drawdowns from behind the dams.

Why is it a Noxious Weed?
Eurasian watermilfoil spreads easily and grows quickly. Eurasian watermilfoil crowds out native plants, reducing biodiversity, diminishes fish habitat and negatively impacts wetland habitats. When it dies off in fall, the large biomass depletes the dissolved oxygen in the water through its decomposition process. Dense mats form near the surface.  They entangle boat propellers and interfere with swimming and fishing activities.

Control Recommendations:
WA State Noxious Weed Board
King County Noxious Weed Board - Best Management Practices
PNW Pest Management Handbook

Click hereto learn more about how we have addressed Eurasian watermilfoil in Mineral lake.