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Aquatic Invasive Species of Concern

Please help us to keep these invaders out!

The best way to prevent the spread of Aquatic Invasive Species is to properly Clean Drain and Dry your watercraft and gear everytime you leave the water.



Zebra Mussels (Dreissena polymorpha) and Quagga Mussels (Dreissena rostriformis bugensis)

Dreissenid Mussels are an invasive species originally from Eurasia in the Caspian Sea region.  These invasive mussels are thought to have come to the US in ballast discharge water from transoceanic ships.  They were first found in the Great Lakes in the early 1990's.  Since then these invaders have been transported and took hold in water bodies all throughout the eastern states.  Microscopic mussel larvae known as Veligers can survive in small amounts of water and be transported from on water body to another.  The best way to prevent the spread of invasive mussels it to thoroughly Clean, Drain and Dry your vessel every time you leave the water.

In 2007 Quagga Mussels were discovered in Lake Mead NV.

Invasive mussels have byssal threads which can attach to any hard surface.  They attach in such high densities in a process known as biofouling that they can damage boat motors, clog pipes, damage pumps, etc.

Invasive mussels are voracious filter feeders.  Phytoplankton and Zooplankton are the basis for the aquatic food web.  Small fish like Tui-chub feed on plankton and the larger Lahontan Cutthroat Trout feed on the Tui-Chub.  In high densities these invasive mussels can decimate plankton populations and lead to an overall decrease in fish populations or in extreme cases total food chain collapse.

As they feed, quagga and zebra mussels accumulate toxins, with some pollutants occurring in their tissues (and their pseudofeces) in concentrations measuring many thousands of times higher than in the surrounding water. Those toxins (including Clostridium botulinum) get passed up the food chain in a process called biomagnification.  As the pseudofeces decomposes oxygen is required; meaning in high densities mussels will also reduce oxygen levels in the water which is harmful to fish and other organisms.

Invasive mussels can increase water clarity allowing sun light to penetrate deeper in the water column, which in turn leads to higher densities of aquatic plants which can clog up water ways and get in the way of recreational fishing.  This deeper penetration of sunlight into the water column could potentially cause the warming of the water column which could push the thermocline into deeper water.  With fish holding at a greater depth, early and late in the fishing season, this could lead to an increased mortality rate for catch and release anglers who may not be familiar with releasing fish safely to deep water particularly during the warm months

Help Prevent the Spread of Invasive Species by Clean, Drain, and Drying your boat every time you leave the water!

Source: Benson, A.J., Raikow, D., Larson, J., Fusaro, A., Bogdanoff, A.K., and Elgin, A., 2022, Dreissena polymorpha (Pallas, 1771): U.S. Geological Survey, Nonindigenous Aquatic Species Database, Gainesville, FL,, Revision Date: 7/19/2022, Access Date: 12/5/2022


New Zealand Mudsnails

Potamopyrgus antipodarum

New Zealand mudsnails (NZMS) are tiny, aquatic snails that reach, on average, up to 4-6 mm long in the western United States. The mudsnail has an elongated, right-handed coiling shell, usually consisting of 5-6 whorls, though some have up to 8. Shell color tends to vary from gray to light or dark brown. This species is ovoviviparous and parthenogenic, meaning they are live-bearers, which release live young rather than eggs, and those offspring are clonal (genetically identical) females that are asexually reproduced. When born, offspring already contain developing embryos within their reproductive system. Upon reaching maturity at 3 mm, females can produce 230 new females per year; estimates indicate that one snail and its offspring can result in over 2.7 billion snails within 4 years. Though sexually reproductive males (<5% of the population) and females do exist in their native range, the populations in the western U.S. are believed to contain only clonal females.  New Zealand Mudsnails have an operculum or "trap door" so to speak, so that they may close their shell and survive out of water for up to 7 days.

New Zealand Mudsnails can reproduce in high densities and out compete other aquatic insects.  Though fish can eat New Zealand Mudsnails, the mudsnail can close its operculum and pass through the fish undigested and unharmed, providing no nutrition for the fish.  

New Zealand Mudsnails are often spread by clinging onto wading boots and felt soles of anglers.  That is why Clean Drain and Dry is important for shore angler was well as boaters!

Source: Benson, A.J., R.M. Kipp, J. Larson, and A. Fusaro, 2022, Potamopyrgus antipodarum (J.E. Gray, 1853): U.S. Geological Survey, Nonindigenous Aquatic Species Database, Gainesville, FL,, Revision Date: 11/1/2022, Access Date: 12/5/2022

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Asian Clams

Corbicula Fluminea

Small bivalved mollusk with distinct concentric ridges running the length of the shell.  Asian clams are often greenish/yellow in color, but could also be a light brown color.  Sizes range from less than 5 mm to less than 50 mm.  Asian clams are hermaphrodites that can reproduce with themselves, causing large population explosions each year.  Asian clams have byssal threads that they can use to cling onto surface or like a parachute float along in the water column.  

Originally from southwestern Asia west to the eastern Mediterranean; Also found in much of Africa and parts of Australia.  The clams are thought to have been brought over unintentionally along with the importation of the Giant Pacific oyster also from Asia.  One speculation is that these clams were brought over by immigrants from their native regions to be used as a food source, although there is no actual evidence for this.

Since arriving in the states, the most economically costly impact has been the biofouling or clogging of pipes and infrastructure.  Power plants draw in raw water along with the clam larvae and these clams can then mature and grow inside the infrastructure of power plants causing expensive clogs which damage equipment and require costly maintenance.  Asian clams degrade overall water quality and are responsible for a decline in dissolved oxygen levels, which are critical for fish spawning habitat.  Native fish such as Lahontan Cutthroat Trout tend to prefer chironomids in the river and dont eat the Asian clams.  Carp however with their pharyngeal jaws that are built for crushing shells, can utilize Asian clams as a food source.

To prevent the spread of Asian clams be sure to Clean Drain and Dry your waders and other gear in between water bodies.  Check out our video on how to Clean Drain and Dry your waders in the "Video" section of this Website!

Source: Foster, A.M., Fuller, P., Benson, A., Constant, S., Raikow, D., Larson, J., and Fusaro, A., 2022, Corbicula fluminea (O. F. Müller, 1774): U.S. Geological Survey, Nonindigenous Aquatic Species Database, Gainesville, FL,, Revision Date: 4/28/2022, Access Date: 12/6/2022

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Signal Crayfish AKA Crawdads

Pacifastacus leniusculus

Originally from the Pacific Northwest and Columbia River region, signal crayfish were introduced by humans into the Truckee River and Lake Tahoe as early as 1895 and 1909 respectively.  Signal Crayfish often (but not always) have a white patch on the back of their claws or chelae, near the hinge. 

Signal Crayfish have been associated with a decline in benthic macroinvertebrate diversity and abundance.  Signal Crayfish also are carriers of the Crayfish Plague which they themselves are immune to but is fatal to other species of crayfish.

To prevent the spread of the Signal Cray, please release all crayfish into the same waterbody that you got them from, do not take any creature from one waterbody and put it in a different one as this could be harmful to the environment and is usually illegal.

Source: Procopio, J., 2022, Pacifastacus leniusculus (Dana, 1852): U.S. Geological Survey, Nonindigenous Aquatic Species Database, Gainesville, FL,, Revision Date: 9/14/2021, Access Date: 12/6/2022


American Bullfrog

Lithobates catesbeianus 

The American Bullfrogs native range is primarily the eastern United States, both north and south, extending as far west as Texas, Oklahoma, Nebraska and South Dakota.  This amphibian invader likes to inhabit lakes, ponds, cattle tanks, bogs, and sluggish portions of streams and rivers.  Throughout the 1900's Bullfrogs were stocked as a food source, subsequent escape and release has helped spread this species throughout the U.S. and worldwide.

Outside of its native range, the American bullfrog has no natural predators and is able to reproduce very rapidly; Female bullfrogs can lay up to 20,000 eggs at a time, whereas most native frog species only lay between 2,000 to 5,000 eggs at a time.  This allows bullfrogs to easily out-compete native amphibians in terms of population.  Adult Bullfrogs are voracious predators that will eat literally anything that will fit in its mouth.  Bullfrogs eat lizards, snakes, birds, bats, mice, turtles, other frogs, and even their own young!  Bullfrogs are known to carry the harmful chytrid fungus which is fatal to other amphibian species.    

The best way to prevent the spread of bullfrogs is to be sure not to release any bullfrogs or other animals into the wild.  Releasing animals into the wild is often harmful to the environment and illegal!

Source: Liz McKercher, and Denise R. Gregoire, 2022, Lithobates catesbeianus (Shaw, 1802): U.S. Geological Survey, Nonindigenous Aquatic Species Database, Gainesville, FL,, Revision Date: 12/2/2022, Access Date: 12/6/2022


Eurasian Watermilfoil

Myriophyllum spicatum

Eurasian Watermilfoil is an aquatic weed that grows in dense mats, native to Europe, Asia and Africa, was likely brought to the U.S. intentionally for aquarium and aquatic nursery trade.  

Eurasian Watermilfoil can be spread by seed or through a process known as fragmentation.  A fragment of the stem can start an entirely new root structure at the node, and then developed into an entire infestation.  Fragments clinging onto boats, fishing gear, or other human means are also a way that this plant can spread.

Eurasian watermilfoil is highly detrimental to native plant species.  Eurasian watermilfoil forms dense mats that shade nearby vegetation preventing other plants from receiving necessary sunlight thus smothering them out them.  As a food source Eurasian watermilfoil provides significantly less nutrition than the plants it replaces.  Eurasian watermilfoil forms dense mats than can disrupt or ruin swimming areas, boating, or fishing opportunities.  In Lake Tahoe, Eurasian watermilfoil provides habitat for warm water invasive fish species such as large mouth bass, blue gil, and gold fish.

Source: Pfingsten, I.A., L. Berent, C.C. Jacono, and M.M. Richerson., 2023, Myriophyllum spicatum L.: U.S. Geological Survey, Nonindigenous Aquatic Species Database, Gainesville, FL,, Revision Date: 3/16/2023, Access Date: 3/29/2023


Curly Leaf Pondweed

Potamogeton crispus

Curly Leaf Pondweed is a rooted, submerged, aquatic plant.  As its name implies it has wavy curly leaves that resemble a lasgna noodle.  Leaves grow about 2-4 inches long.  Usually greenish-brown in color, this plant can also be reddish as well.

Originally from Eurasia, Africa and Australia, Eurasian watermilfoil likely arrived here through the migration of waterfowl.  It has spread throughout the country likely as a result of waterfowl migration, may have been stocked for waterfowl habitat and in water from fish stocking.

Curly leaf pondweed can tolerate very low light levels, very low water temps, and thrives in polluted waters.

Once water temps rise above 10 degrees Celsius this plant will exhibit very rapid growth, expanding and out competing native plants which tend to bloom out a little later in the season.

 Curly leaf pondweed forms dense mats that out compete native vegetation, clog up waterways inhibiting activities such as fishing, boating, and swimming.

To help prevent the spread of curly leaf pondweed please be sure to Clean Drain and Dry all waders and gear between waterbodies.

Source: Thayer, D.D., I.A. Pfingsten, L. Cao, and L. Berent., 2022, Potamogeton crispus L.: U.S. Geological Survey, Nonindigenous Aquatic Species Database, Gainesville, FL,, Revision Date: 3/18/2016, Peer Review Date: 2/9/2016, Access Date: 12/12/2022

Aquatic Invasive Species of Concern: Meet the Team
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