Eurasian Watermilfoil
Category
Invasive Macrophyte
Common Name
Eurasian Watermilfoil
Species Name
Myriophyllum spicatum
Distribution / Status (Lake Tahoe)
Established invasive (Tahoe Keys, Emerald Bay, South shore); common in marinas
Diagnostic Features
Whorls of 4 leaves, 12–21 leaflet pairs, dense mats, brittle stem fragments
Commonly Confused Species
Andean Milfoil (Myriophyllum quitense); Coontail (Ceratophyllum demersum)
Growth Form
Submersed perennial macrophyte
Leaf Shape
Feathery, threadlike, finely divided leaves with 12–21 leaflet pairs
Leaf Arrangement
Whorls of 4 (rarely 3–5) around stem
Leaf Size
1.5–4 cm long; leaflets ~0.5–2 mm wide
Leaf Margin
Smooth; divisions very fine and uniform
Leaf Apex & Base
13-25 paired leaflets evenly spaced along rachis
Venation Pattern
Thread-like veins, single midrib per leaflet
Stem Structure
Long, smooth stem; branching near surface, slender, often reddish-brown near tip
Plant Height
0–8 m
Roots / Rhizomes
Fibrous, rooted in soft sediment
Habitat Type
Lakes, reservoirs, marinas, canals; tolerant of disturbance
Depth Range
0.5–10.5 m, optimal around 2–3 m
Substrate Preference
Sand, soft, silty, nutrient-enriched sediments
Light Preference
High light preferred; tolerates some turbidity
Ecological Role / Impact
Forms dense mats; shades out natives; alters oxygen and nutrient cycles; impedes boating
Flowers (Reproductive Structures)
Small emergent spikes 2–6 cm long with reddish flowers; pinkish
Reproductive Strategy
Vegetative fragmentation dominates; each fragment can root
Buoyancy / Adaptations
Highly flexible stems form dense surface mats
Color
Bright green to reddish brown
Texture
Soft, pliant, delicate
Growth Rate / Seasonality
Rapid growth; early spring emergence, persists through summer
References
DiTomaso, J. M., & Kyser, G. B. (2013). Eurasian watermilfoil. In Weed Control in Natural Areas in the Western United States Eurasian watermilfoil (pp. 544–547).
Lewis County Noxious Weed Control Board. (n.d.). Eurasian watermilfoil. Lewis County Government. Retrieved from https://lewiscountywa.gov/departments/weed-control/identification/aquatic-riparian-noxious-weeds/eurasian-watermilfoil/
Prather, T. S., Robins, S., Daniel, S., & Laitala, K. (2003). Eurasian watermilfoil Identification and management in Idaho. University of Idaho.
Vermont Aquatic Invasive Species Program. (n.d.). Aquatic Plant Characteristics: Eurasian watermilfoil vs. Native Look-Alikes. Vermont Aquatic Invasive Species Program.
Supporting Partners
The Martis Fund, a collaborative project of Martis Camp landowners, DMB/Highlands Group (the developers of Martis Camp), Mountain Area Preservation (MAP), and Sierra Watch. (See martisfund.org for more information)
The Community Impact Fund, Ashley Quinn Fund & the Foresight Fund held at the Tahoe Community Foundation
Additional thanks to the Tahoe Regional Planning Agency for providing specimens for studio filming
