Tools to Identify Aquatic Invasive Species

Need a field guide?

There are many great AIS identification books for free and for sale. Washington Department of Ecologyhaspublished An Aquatic Plant IdentificationManual, available for free online or Aquatic and Riparian Weeds of the Westis available for purchase.

This easy-to-use photo page shows 6 possibleAIS that might be found in lakes and slow moving water bodies. It can be used to identify common characteristics of the plants.

Below are some aquatic invaders to be on the lookout for:

Photo Identification Section
Zebra and Quagga Mussels

Dreissena bugensis (Quagga) and Dreissena polymorpha (Zebra) are destructive invasive aquatic species native to the Ukraine and Russia. These mussels are highly destructive in freshwater systems because they can:

  • Reproduce quickly and in very large numbers, up to 1 million larvae per spawning season.
  • Colonize on both hard and soft surfaces, from the water's surface to more than 400 feet down, including boat hulls, propellers, anchors, docks, and boat trailers.
  • Coat submerged surfaces such as piers, pilings, rocks, cables, boat ramps, docks, lines, pipes and fish screens which increases operation and maintenance costs.
  • Infiltrate and damage boat engines, bilges, live wells, and steering components.
  • Threaten the state's municipal water supplies hydroelectric plants, reservoirs and irrigation systems.
  • Clog municipal water intake structures and obstruct the flow of drinking water.
  • Cost taxpayers millions of dollars to repair damaged pipes and water transport facilities.
  • Wreak havoc on the environment by disrupting the food chain by filtering the water column of phytoplankton and depriving fish of a food source.
  • Change water conditions, causing heavier aquatic plant growth, oxygen loss, and fish kills.
  • Result in infested waters being closed to boating and fishing altogether.
    Quagga/Zebra mussels pose serious risks and costs to you as a boat owner because they can:
  • Ruin your engine by blocking the cooling system and causing overheating.
  • Increase drag on the bottom of your boat, reducing speed, and wasting fuel.
  • Jam your boat's steering equipment.
  • Require you to scrape and repaint your boat's hull.

Only freshwater mussel in North America that clings to substrate (If you see a striped mussel attached to anything, it is likely a zebra or quagga mussel) REPORT IT!!!
Striped shell
Adults range in size from the size of a grain of rice to one inch.



Montana ANS Priority Class 1
Egeria densa

Aquatic plant from South America, Brazillian elodia was imported from the aquarium trade. It has few natural predators to keep its growth in check and can displace native plants. Once introduced it can form dense mats that are unsightly, interfere with recreation, and degrade fish habitat.

General Characteristics:

  • Similar to hydrilla
  • Submersed aquatic weed, found in ponds, lakes, streams and rivers
    May reach 6 feet in length and are freely branching
  • Leaves occur in whorls of 3-6, most commonly 4
    Individual leaves are 1-1 inch long, 5 mm wide
  • Finely toothed leaf margins
  • Undersides of the leaf midribs are smooth and without teeth unlike those of hydrilla
  • Flowers have 3 white petals and 3 green sepals
  • Flowers appear at water surface on long stalks, showy flowers petals are 1/3 inch long


Montana ANS Priority Class 1
Hydrilla verticillata

Introduced from Asia for use in aquariums, this plant spreads by fragmentation and via transport on boats, motors, trailers, fishing nets and other gear, and aquarium or water garden release.

General Characteristics:

  • Grows thick mats especially in shallow water
  • Quickly takes over shallow lakes and rivers, preventing boating, fishing, hunting, and swimming
  • Clogs irrigation canals
    Difficult to identify, sometimes confuse with Elodea or Egeria
  • Sharply toothed leaves in whorls of 3-8
  • Sometimes possess small teeth along underside of leaf midrib

    Eurasian Watermilfoil

    Montana ANS Priority Class 3

    Myriophyllum spicatum

    Eurasian watermilfoil, right, is much denser than native norther watermilfoil, left.

    General Characteristics:

    • Spreads by fragmentation, currents and waves, and overland via transport on boats, motors, trailers, fishing nets, and other gear
    • Grows thick mats in waters less than 15 deep
    • Eradication is nearly impossible
    • Can quickly take over shallow lakes and rivers, which can prevent boating, fishing, hunting, and swimming
    • Submersed, perennial, aquatic plan with feathery leaves arranged in whorls around the stem.
    • Found growing in shallow water to 25 feet deep or more.
    • Tops often turn read in color.
    • Milfoil stems branch several times near the water surface.
    • Erect stalks emerge above water with small reddish flowers.
    • Typically 4, but sometimes 3-5 leaves, form a whorl around the stem.
    • Each leaf has 12 or more pares of leaflets.

    Curlyleaf Pondweed
    Montana ANS Priority Class 4
    Potomogeton crispus

    This plant is native to Eurasia, Africa and Australia. By 1950 most of the U.S. was infested by this species. Curlyleaf pondweed forms dense mats which interfere with recreation and limit the growth of native aquatic plants. In shallow lakes it can grow dense enough to affect recreational boating and fishing. It can alter nutrient dynamics of a fertile lake causing heavy summer algal blooms.

    General Characteristics

    • Leaves are alternate with crinkled leaves that are finely toothed
    • Most often found in ponds with fertile, hard water
    • Flower spikes often stick up above the water surface during spring
    • Tolerates low light and may grow in deep water

    Flowering Rush

    Montana ANS Priority Class 4
    Butomus umbellatus

    An emergent in shallow areas of lakes, flowering rush has umbellate pink flowers and grows to 3 feet tall on triangular stems. Flowering rush was introduced as an ornamental.

    General Characteristics:

    • Flowers grow in umbrella shaped clusters and each individual flower has 3 whitish pink petals
    • Plants only produce flowers in very shallow water or on dry sites
    • Green stems resemble bulrushes but are triangular in cross section
    • Leaf tips may be spirally twisted
    • Along shores, has erect leaves and grows to about 3 feet in height
    • Forms an extensive root system that can break into new plants if disturbed
    The Flathead Basin Commission, Protecting water quality since 1983


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    Caryn Miske Executive Director
    Flathead Basin Commission
    655 Timberwolf Parkway
    Kalispell Montana 59901
    406-240-3453 e-mail: cmiske@mt.gov


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