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Lake Weed Identification

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The following  picture common aquatic weeds throughout the country. Place your weed in a clear glass jar with water and compare it to the pictures. Pay careful attention to the leaves. (It's really not that difficult!)

If you are unable to identify your weed(s) consider these options:
  1. Contact your local Fish and Game or County Extension Agent.
  2. Contact a local College or University.
  3. Talk to your neighbors.

weed photo

Eurasian watermilfoil
(Myriophyllum spicatum)

Class B Noxious Weed

Eurasian watermilfoilHistory

Milfoil originates from Europe and Asia, but was introduced to North America through the aquarium industry. Milfoil may have arrived as early as the late 1800s, but was first documented in the Eastern United States in the 1940s.

Method of Spread

Milfoil forms very dense mats of vegetation on the water's surface, impairing water recreation. It spreads rapidly, mostly by fragmentation of plant parts. In the late summer and fall, the plants become brittle and naturally break apart. Each fragment is capable of growing roots and developing into a new plant. It is competitive with native species and may completely dominate a plant community within a few years.

Milfoil is widespread throughout western Washington and Oregon. Found in Lake Meridian near Seattle in 1965 and Lake Washington by the mid-1970s. The distribution of milfoil now closely follows Interstate 5. Milfoil has probably been spread from lake to lake on boat trailers.

Methods of control

Once milfoil is well-established, it is difficult to eradicate. In smaller lakes, aquatic herbicides have been partially successful. Other control methods include: underwater rototilling, bottom barriers, hand pulling or dredging, and in limited situations, sterile grass carp. Removing fragments from boat trailers and along shorelines is advised to prevent milfoil's spread into new areas.


  • submersed aquatic milfoil grows in dense mats, with stalks of tiny reddish flowers held above the water
  • usually has twelve or more leaflet pairs on each leaf
  • mature leaves are usually arranged in whorls of four and are about three cm long
  • leaves rarely extend above the water and collapse when removed from the water
  • stems may reach lengths of three m or more, are usually two - four mm thick, and are reddish to olive green
  • blooms June to August

MILFOIL (Myriophyllum)

Leaves whorled in groups of four. Each leaf is divided into many thread-like leaflets extending from a central rib (see leaf detail). Forms tangled mats at the surface. Seed heads develop in mid to late season and may extend above the water surface. Treat when weeds are actively growing before flowering occurs.


ELODEA (Elodea canadensis)

Broad oval leaves, usually four in number, arranged in whorls around the stem. Whorls are compact near the growth tip with spacing between the whorls gradually increasing further down the stem.


LARGE-LEAF PONDWEED (Potamogeton amplifolius)

Leaves both floating and submersed. Submersed leaves are large, oblong, wavy, and taper to the stem. Floating leaves are oval-shaped. Parallel leaf veins are evident. Stems are seldom branched. Leaves alternately arranged on stem. Solid, tightly packed spike of nutlets at tip of weed rises above water surface.




WATER SHIELD (Brasenia schreberi)

Leaves are oval in shape with smooth edges. Stem is attached to the middle of the leaf. Rust colored underside. A clear jelly-like coating covers the underside of the leaves and stems on mature weeds. A dull purple flower develops in early summer. Treat before jelly-like coating develops.

PARROT FEATHER (Myriophyllum Brasiliense)

Also a type of Milfoil. Leaves whorled in groups of four to six. Each leaf is divided into eighteen pairs of thread-like segments resembling a feather (see leaf detail). This species differs from other Milfoils by having its foliage partially out of the water. Emersed foliage is bright green.

HYDRILLA (Hydrilla verticillata)

Stem is long and branched with oppositely arranged leaves at the bottom and whorls of 3 leaves on the upper portion of the plant. Leaf is oval-shaped with margins toothed. There are pointed spines on the mid-rib of the underside of the leaf.

FLOATING-LEAF PONDWEED (Potamogeton natans)

Leaves both floating and submersed. Submersed leaves are long and narrow. Floating leaves are oblong and slightly heart-shaped at base. Parallel leaf veins are evident. Stems occasionally branched. Leaves are alternately arranged on stem. Solid, tightly packed spike of nutlets at tip of weed rises above water surface.





WHITE WATER LILY (Nymphaea odorata)

Leaves large, round and slit to the center. Underside of leaf is often purplish. Stem is below the surface. Roots are thick and fleshy, most often buried in mud. Flowers are white with multiple rows of petals born on a single stalk at or above the surface. May be confused with Spatterdock.

COONTAIL (Ceratophyllum demersum)

Leaves whorled around the stem and have a serrated appearance (see leaf detail). Spacing between leaf whorls is variable. Consequently, weeds may be long and sparse or bushy. Near the end of the stem leaves and whorls are crowded. Branches are forked repeatedly. Do not confuse with Chara.

CLASPING-LEAF PONDWEED (Potamogeton richardsonii)

Leaves wide and wavy with smooth edges. Broad base clasps the stem. Upper stem commonly branched and leafy. Leaves are alternately arranged on stem. Solid, tightly packed spike of nutlets at tip of weed rises above water surface.


BUSHY PONDWEED (Najas gracillima)

Leaves are narrow with tiny spines along the edges. Slightly enlarged at the base. Stems slender with frequent branching. Leaves oppositely attached, or in groups of two or more at a node. Leaves are densely concentrated at the tips. May be confused with Chara. Chara has a strong odor when crushed, Bushy Pondweed does not.


FALSE LOOSESTRIFE (Ludwigia palustris)

Leaves both floating and submersed. Oblong and narrow near the stem. Leaves oppositely attached to stem, most often in pairs. Stems rooted at the joints. Forms tangled mat on the surface.


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