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Listed below are some of the top aquatic invasive species (AIS) for which we are constantly monitoring our lakes.

If you have noticed any of these species while you’ve been out on our waterways, please fill out the brief AIS form – it will alert the appropriate people at Montana Fish, Wildlife and Parks so they can follow-up. Thank you for your support.

American Bullfrog

American Bullfrog

American Bullfrog (Lithobates catesbeianus) is the largest true frog native to the Eastern United States. It is non-native to Montana but has been detected in Montana and tied to the decline of native frogs, turtles and waterfowl production. They are indiscriminate feeders and will eat anything smaller than themselves.

Adults range in size between 9 and 15.2 cm (snout vent length). They are identified by their green or olive smooth skin, often with dark mottling on their backs, and a cream underbelly.  The back of the thighs are flecked with small light spots. The hind feet are webbed with the longest toe extending past the webbing. Adults can be identified by their loud, deep call which can be heard from a considerable distance. Tadpoles can be differentiated from other frog species by their large size (approximately 15 cm), olive green color, scattered black dots, and lack of visible intestinal coil.

In Montana, bullfrogs breed during warm weather in June and July and eggs hatch in 4 or 5 days.   You can stop the spread of this species by not purchasing or releasing pet bullfrogs, and by reporting any field observations to your local Fish, Wildlife & Parks office.

Asian Clam

Asian Clam

The Asian Clam (Corbicula fluminea) is a species of freshwater clam native to eastern Asia which has become a successful invasive species throughout North America, South America, and Europe. The Asian clam is a filter feeder that removes particles from the water column. It can be found at the sediment surface or slightly buried. Its ability to reproduce rapidly, coupled with low tolerance of cold temperatures (2-30°C), can produce wild swings in population sizes from year to year in northern water bodies.

They are small, averaging less 1.5 inches, with light green or light brown shells. They prefer quiet water with low salinity and sandy substrates, but can thrive in brackish water bodies. They generally prefer to colonize near shore. They are thought to occasionally self fertilize and the young are hatched in the spring and usually attain sexual maturity by fall and may live up to seven years.

Some tips to help identify native species from the invasive Corbicula. An overall good rule of thumb to remember is Corbicula are about nickel to half dollar in size, triangular to subtriangular in shape, whereas native mussels are larger than a half dollar, oval to quadrangular or subquadrangular in shape.

Chinese Mystery Snail

Chinese Mystery Snail

Chinese Mystery Snail (Cipangopaludina chinensis) has become a problematic invasive species in many areas and an introduced species in the United States. This species can be identified by their relatively large globose shells reaching 2.5 in. in height and exhibiting light coloration as a juvenile and olive green, greenish brown, brown or reddish-brown pigmentation as an adult. This species prefers freshwater lakes with soft, muddy or silty bottoms, reservoirs, slow-moving freshwater rivers, streams, and ponds with aquatic grass.

These snails are popular in freshwater aquariums because they do not eat fish eggs or plants, they do not overpopulate the aquarium, and they close up if there is a water problem, giving people an indication that something is wrong a few weeks before the fish die.

Curly-Leaf Pondweed

Potamogeton Crispus

Curly-leaf pondweed (Potamogeton crispus) is an aquatic perennial native to Eurasia, Australia, and Africa. The leaves of this rooted, submerged plant are olive green to red-brown, oblong, and finely toothed with wavy margins (~ 8cm long and 1.5 cm wide). Leaf tips are rounded, and stems are flat and alternately branched. Typically found in water less than 3 meters deep, it is tolerant of low light and low water temperatures and can be found up to 18 meters deep.

Inconspicuous, unbranched, and erect flower spikes of 1-2 cm long grow above the water surface in spring to early summer. The majority of reproduction occurs from turions (burr-like winter stem buds) that are present in fall and winter and are usually terminal on a stem or in leaf axils.

The early spring growth of Curly-leaf Pondweed shades-out and inhibits native aquatic plants. This growth can result in dense mats that inhibit boating and swimming. Once the plant dies-back (becomes dormant) in mid-summer, the decay depletes oxygen in the water, potentially encouraging algal blooms.

Eurasian Watermilfoil

Myriophyllum Spicatum

Eurasian watermilfoil (Myriophyllum spicatum) is a submersed aquatic plant native to Europe, Asia, and northern Africa. Like the native milfoils, the Eurasian variety has slender stems whorled by submersed feathery leaves and tiny flowers produced above the water surface. The flowers are located in the axils of the floral bracts, and are either four-petaled or without petals.

The leaves are threadlike, typically uniform in diameter, and aggregated into a submersed terminal spike. The stem thickens below the inflorescence and doubles its width further down, often curving to lie parallel with the water surface. The fruits are four-jointed nut-like bodies. Eurasian watermilfoil has 9-21 pairs of leaflets per leaf, while Northern milfoil typically has 7-11 pairs of leaflets. Coontail is often mistaken for the milfoils, but does not have individual leaflets. Leaf tips are rounded, and stems are flat and alternately branched. Typically found in water less than 3 meters deep, it is tolerant of low light and low water temperatures and can be found up to 18 meters deep. Inconspicuous, unbranched, and erect flower spikes of 1-2 cm long grow above the water surface in spring to early summer.

The early spring growth of Curly-leaf Pondweed shades-out and inhibits native aquatic plants. This growth can result in dense mats that inhibit boating and swimming. Once the plant becomes dormant in mid-summer, the decay depletes oxygen in the water, potentially encouraging algal blooms.

Faucet Snail

bithynia tentaculata

The Faucet Snail (Bithynia tentaculate) is a nonnative snail to Montana. It has a shiny pale brown shell with a relatively large, rounded spire. Shell is usually no larger than 12-15 mm and is sexually mature by the time it reaches 8mm in size.

The faucet snail typically competes with native snails due to its high growth rates and its ability to filter feed. This species has been known to infest municipal water supplies and has the potential to bio-foul underwater intakes and infest swimming areas.

Its native range is in Europe, from Scandinavia to Greece. It has been detected in Montana.

Flowering Rush

Flowering Rush

Flowering Rush (Botomus umbellatus) is a perennial aquatic herb that emerges each spring from winter-hardy rhizomes. Emergent leaves are stiff, narrow, sedge-like (3-edged or triangular in cross-section) and up to 3 feet above the water surface. In deep water, the plant can be entirely submerged. Submerged plants have limp leaves and do not flower. Often unnoticed among other wetland plants until it blossoms, flowering rush has a distinctive spray of attractive white, pink, or purple flowers on a tall stalk. Blooming in late summer to early fall, flowers have 3 petals, 3 sepals and red anthers.

Fragrant Water Lily

Nymphaea Odorata

Fragrant Water Lily (Nymphaea odorata) is an aquatic plant with large, radially symmetrical white or pink blooms and heart-shaped glossy green floating leaves with a purple underside. The leafstalk is submerged grows out of large rhizomes which serve as a common food source for muskrats .The flowers range from 3-15 inches wide with several broad, curved petals that narrow toward the center. The center has one pistil that is densely packed with bright yellow stamens.

They are found in still, relatively shallow water (5-7 ft.) in water bodies such as lakes and ponds with silty beds. It is the most common white water lily. Native to the eastern portion of North America, its commercial popularity has caused its extensive dispersal throughout North America. The plant is now considered a secondary invader that can achieve extraordinary population growth and destabilize ecosystems.

Golden Mussels

Golden mussel

Golden mussel (Limnoperna fortunei), an invasive, non-native freshwater/brackish bivalve, was recently discovered in the Sacramento – San Joaquin Delta. This discovery is the first known occurrence of golden mussels in North America. The species poses a significant immediate threat to the natural ecosystems, water conveyance systems, infrastructure and water quality in California and across the U.S. Golden mussels are similar in appearance, biology, and impacts to quagga and zebra mussels, but can establish in waters with considerably lower calcium levels than required by quagga and zebra mussels.

They are small, typically under 1.5 inches in length. Shell color is light golden to darker yellowish-brown to brown color and can thrive in freshwater and brackish water and inhabit shallow aquatic environments. Shortly after fertilization, the larvae become mobile; capable of coordinated swimming and they disperse in the water column. Once a suitable substrate is found, the mussels attach themselves to the substrate by byssal threads and begin developing into adults. Maturity is reached when the mussel attains a length of approximately 5.5 mm (almost ¼ inch) which occurs within the first year of its lifespan. Golden mussels can grow in dense clumps or colonies containing as many as 80,000 -200,000 organisms per square meter.

New Zealand Mudsnail

Potamopyrgus antipodarum

The New Zealand mudsnail (Potamopyrgus antipodarum) is a small aquatic snail.  As its name states, this species is native to freshwater lakes and streams of New Zealand.  Like many organisms today, it is being incidentally carried to many locations around the world such as Europe, Asia, and North America. In the U.S., this snail was first detected in the mid-1980s in the Snake River region of Idaho.  Since then, it has spread to waters of Montana, Wyoming, California, Arizona, Oregon, and Utah. They have even found their way into the waters of Yellowstone National Park.  The only known population in the eastern U.S. is in Lake Ontario where a population was discovered in the early 1990s.

Mudsnail densities of over one-half million per meter square in western streams are a cause for concern. Because the West is known for abundant trout and productive fishing spots, there is concern that the mudsnails will impact the food chain for native trout and the physical characteristics of the streams themselves.  Research is needed to determine the impacts of large populations of mudsnails on the native fauna, such as aquatic insects and native snails, and on any changes in the physical environment.

Quagga Mussel

Quagga mussel

The Quagga mussel (Dreissena bugensis) is a mollusk native to parts of Ukraine. This small freshwater mussel is an active filter feeder, which competes for food resources with filter-feeding zooplankton by accelerating sedimentation of suspended matter, including organic substances. It is also a nuisance and economic problem when it grows on recreational or commercial ships/boats, potable water treatment plants and electric power stations. Quagga mussels commonly have alternating light and dark brown stripes, but can also be solid light brown or dark brown. They have two smooth shells that are shaped like the letter “D”.

These mussels are usually less than 2 inches in length. In new populations, most mussels are young and therefore very small (under ¼ inch long). There are two phenotypes of D. bugensis that have been reported in the Great Lakes: the “epilimnetic” form, which has a high flat shell, and the “profunda” form, which has an elongate modioliform shell and has invaded soft sediments in the hypolimnion. The epilimnetic form uses its byssal threads to attach to objects and particles and form druses or colonies. The profunda morph can form colonies and attach to objects with its byssal threads or it can partially bury itself in soft sediments and extend its very long incurrent siphon above itself to bring in suspended food particles.

Zebra Mussel

Zebra Mussel

The Zebra mussel (Dreissena polymorpha) is a tiny (1/8-inch to 2-inch) bottom-dwelling clam native to Europe and Asia. Zebra mussels were introduced into the Great Lakes in 1985 or 1986, and have been spreading throughout them since that time. They were most likely brought to North America as larvae in ballast water of ships that traveled from fresh-water Eurasian ports to the Great Lakes. Zebra mussels look like small clams with a yellowish or brownish D-shaped shell, usually with alternating dark- and light-colored stripes. They can be up to two inches long, but most are under an inch. Zebra mussels usually grow in clusters containing numerous individuals.