Aquatic nuisance plants and animals (sometimes called nonnatives or exotics) threaten the Lake Champlain Basin's native fish, wildlife, and plants and impede recreational activities. Sometimes, they have substantial ecological and economic impacts and spread prevention is critical. These species enter Lake Champlain via the Champlain Canal, the Richelieu River and Canal, and over land primarily through human activities such as boating and bait transport. Nonnative species in Lake Champlain were first recorded as early as 1840!

More than four dozen aquatic nuisance species are currently present in the Basin. The following are of particular concern for the Lake and/or high priority species for management in the Lake Champlain Basin Aquatic Nuisance Species Management Plan - 2005 (species indicated by a *).

• Alewife*
• Asian Clam*
• Eurasian Watermilfoil*
• Japanese Knotweed*
• Purple Loosestrife*
• Rusty Crayfish
• Sea Lamprey*
• Tench
• Water Chestnut*
• White Perch
• Zebra Mussel*
• Variable-Leaved Watermilfoil
• Didymo

Recent nonnative introductions that could become nuisances include gizzard shad, and blueback herring. Potential species that could invade the Lake in the near future that are of great concern include: the fish round goby, Eurasian ruffe, quagga mussels, fishhook water flea, spiny water flea, and the plant hydrilla, which can completely clog waterways and can already be found in three New England states. Visit the ANS Threats page to learn more.

The Lake Champlain Basin Program has been a key partner in the development of the Lake Champlain Basin Aquatic Nuisance Species Management Plan - 2005, along with the States and many other groups.

Publications and Websites

• Lake Champlain Basin Aquatic Invasive Species Guide (7.2 MB)
• Aquatic Invaders Brochure (Spread Prevention Tips) (1.5 MB)
• Baitfish of Vermont Including Lake Champlain (VTFWD) (763 KB)
• Nuisance Aquatic Species Article (LC Basin Atlas)
• Aquatic Nuisance Species Bibliographic Database (NY Sea Grant)
• Nuisance Aquatics Links

In 2003, alewives (Alosa pseudoharengus) were confirmed in Lake Champlain when several juvenile fish were found during a yearly forage fish trawl survey by Vermont Fish and Wildlife Department. The number caught in subsequent surveys has increased. In 2008, widespread alewife die-offs occurred in the Lake, confirming that large numbers are now present. Although alewives do undergo periodic mass mortality events, the specific cause of the Lake Champlain die-off is unclear. The full impacts of alewives on Lake Champlain are yet to be realized. Biologists are concerned that the establishment of this exotic fish species in the Lake and other Basin waters could prove to be a major threat to native forage and game fish populations.

The alewife is a marine fish species from the herring family. Native populations of this fish inhabit the Atlantic Ocean. Each spring, adult alewives migrate into freshwater rivers to spawn. The young hatch in the rivers, reside there for the summer, and then migrate out to sea in early fall where they mature as adults. Alewives can, however, survive in freshwater. Alewife populations have become established in Great Lakes and many landlocked lakes in New York, Maine, Connecticut, and other New England states.

Alewife threaten the native species of Lake Champlain by altering zooplankton communities, competing with other fish for food, and feeding on native fish eggs and larvae. They also pose a threat to Lake Trout and Atlantic salmon who can experience reproductive failure when feeding on an alewife diet due to a severe vitamin B deficiency. The alewife in Lake St. Catherine have caused problems, including decreased water clarity and a threatened smelt population. In February 2006, the LCBP and Lake Champlain Sea Grant co-hosted a workshop of technical professionals to assess the potential impacts alewives could have on Lake Champlain. Visit the link below to read the workshop summary.

• Lake Champlain Alewife Impacts: February 14, 2006 Workshop Summary [933 KB PDF]
• Alewife - VT ANR, DEC Aquatic Nuisance Species in Vermont
• Alewife Confirmed in Lake Champlain (VT F&W Press Release, November 10, 2005)

Asian clams

The Asian clam (Corbicula fluminea) was first found in the Lake Champlain Basin in August 2010. After its initial discovery in Lake George by a researcher at Rensselear Polytechnic Institute’s Darrin Fresh Water Institute (DFWI), scientists found that the invasive mollusk had colonized nearly six acres of lake bottom near the Village of Lake George. Experts believe that the clams had been in the lake for two to three years before discovery and had possibly completed four to six reproduction cycles. It is unknown how Asian clam reached Lake George, but potential vectors of introduction include an aquarium dump or live bait.

This hermaphroditic bivalve is native to tropical areas in Asia, the eastern Mediterranean, and Australia. Their shells are brown or yellow-green with thick concentric rings on the outside and smooth with a purple tinge on the inside. They are generally smaller than a penny in diameter, but can reach sizes of up to 5cm. Unlike zebra mussels, which hitchhike on boat hulls and colonize on other hard surfaces, the clams prefer open, sandy areas with limited plant growth. They can form thick mats, and in Lake George have reached densities of up to 600 clams per square meter. Asian clams usually reproduce twice annually with one clam capable of releasing up to 2,000-4,000 offspring each cycle. Water temperatures must rise above 59 degrees Fahrenheit (15 degrees Celsius) for the clams’ reproductive cycle to become active.

The Asian clam is a filter feeder that excretes fecal matter into the water. Research conducted in Lake Tahoe suggests the clams are associated with algal blooms and their presence may change the water chemistry, possibly providing a calcium-rich breeding ground for other potential invasive species such as zebra or quagga mussels. The Asian clam crowds out native species and reduces biodiversity on the lake bottom. Asian clams can clog water intake systems of boats, homes, industry, and municipalities.

The Lake George Asian Clam Rapid Response Task Force was quick to launch efforts to eradicate the clam. A pilot project in Fall 2010 found that the installation of benthic barrier mats on the lake bottom was the most effective method of combating the clams. The 7’ x 50’ PVC mats cut off the oxygen supply and smother the clams. In Spring 2011 scientists and divers installed over 800 mats in the main infestation area and under docks and piers along the shoreline. The Task Force will identify the most appropriate containment strategy based on the effectiveness of the 2011 treatment.

• Lake George Asian Clam Eradication Project

Eurasian watermilfoil (Myriophyllum spicatum), first discovered in the Basin in 1962, is found in many areas throughout the Lake and Basin. In some areas infestations are severe. Detailed watermilfoil studies have been conducted for many of Lake Champlain's bays and for 35 other lakes within the Basin, but many areas have little or no study regarding the presence and extent of infestation. Because Eurasian watermilfoil is spread by plant fragments transported by waves, wind, currents, people, and to some extent, animals, it is not easily controlled.

Controlling Eurasian Watermilfoil is very costly. More than $4.1 million of federal, state, and local funds (excluding salaries and administrative costs), and thousands of volunteer hours have been spent on controls in Vermont lakes and ponds since 1982. Control mechanisms that have been employed in the Basin include mechanical harvesting, diver-operated suction harvesting, installation of bottom barriers, fragment barriers, and handpulling. Lake level drawdown and hydro-raking have been found to be somewhat ineffective in Lake Champlain and biological controls such as the release of a species of aquatic weevil are being studied but have not yet proven successful.

• Eurasian Watermilfoil Article & Maps (LC Basin Atlas)
• Vermont ANR Eurasian Milfoil information

Japanese knotweed (Polygonum cuspidatum) was first introduced to the United States as an ornamental plant in the late 1800s because of its appealing flowers. It was also used for erosion control because of its rapid and prolific growth. It has subsequently spread into the wild across the majority of the United States, including the Lake Champlain Basin. It spreads via underground rhizomes that easily fragment and spread to other areas. This is especially problematic along streambanks and in riparian zones where natural forces contribute to the spread of knotweed.

Japanese knotweed has already altered the natural characteristics of the Lake Champlain Basin's riparian zones. Knotweed grows early in the season and is very dense which excludes the growth of the Basin's native plant species, decreasing diversity and altering wildlife habitat. It is also quickly rebounds from disturbances such as flooding. In the fall, when the plant dies back, the dead stems and leaf litter form a dense mat that decomposes slowly, further inhibiting native plant growth. Dense growth in riparian zones also excludes recreational uses such as swimming, fishing and boat access. When dense stands are removed from river banks there is an increased risk of erosion until native plants are able to reestablish themselves.

While there are several methods to control knotweed, they are expensive and generally require intensive labor and reapplication. Despite the fact that some people enjoy the taste of the young shoots and the appearance of the plant as an ornamental, it is an undesirable resident of the Basin. Spread is important to preserve the natural characteristics of the Basin's riparian zones.

• Japanese Knotweed Alliance Website
• Japanese Knotweed Control Options (University of Georgia / USDA)
• Japanese Knotweed in Vermont PDF Fact Sheet (Nature Conservancy)

Although it adds vibrant swaths of color to the Basin's roadside ditches and wetlands, purple loosestrife (Lythrum salicaria) is an unwanted alien to this region. It crowds out native wetlands and vegetation such as cattails, grasses, sedges, and rushes, and is of little or no value to wildlife. Loosestife is quick to invade many habitats, including wet meadows, marshes, river banks, and the edges of ponds and reservoirs. Gardeners can accidently increase its spread by planting it in home gardens. Even sterile varieties, often sold by nurseries, are now considered a problem and should never be planted.

Purple loosestrife is native to Eurasia and has been present in New England for almost 100 years. Nowadays is can be found throughout the temperate portions of the United States and Canada. It has no natural predators in North America. The VT DEC has been working for several years to determine whether an introduced beetle (Galerucella) which eats loosetrife can help control the plant's spread. This beetle has been placed in several test wetlands throughout Vermont and has shown promising results.

• Purple Loosestrife - VT ANR, DEC Aquatic Nuisance Species in Vermont
• Adirondack Park Invasive Plant Program

The rusty crayfish (Orconectes rusticus) is a species native to Ohio and Tennessee but is spreading to many other parts the country including New York and all New England states except Rhode Island. They have been found in Lake Carmi and were spotted in the lower Winooski River in 2005. Rusty crayfish typically displace or hybridize with native crayfish populations and opportunistically prey on native plants, benthic invertebrates, fish eggs, and small fish. Their aggressive predation of native species decreases diversity, destroys habitat and has an overall negative impact on many aquatic ecosystems. Rusty crayfish may also spread Eurasian watermilfoil by fragmenting the plants and defoliating native flora which clears the way for further milfoil infestation.

There are currently no successful management techniques for rusty crayfish once a population is established.

• Rusty Crayfish Fact Sheet (University of Minnesota)
• Rusty Crayfish Distribution Map (USGS)

Although believed to be a native species, sea lamprey (Petromyzon marinus) populations are currently excessive and problematic. Sea lamprey are parasitic inhabitants of Lake Champlain. Adults spawn in several of the Lake's tributaries, leaving nonparasitic larvae (ammocoetes) to remain in stream sediments for several years until they transform into the adult form, at which point they migrate to the Lake to prey on fish. Attacks by adult sea lamprey on landlocked Atlantic salmon, lake trout and other fish species have limited the full development of a Lake Champlain fishery, and restricted recreational and associated economic opportunities. Studies from the Great Lakes show a 40-60% mortality rate for fish wounded by sea lamprey.

A long-term control program began in 2002 following the evaluation of an eight-year experimental program. Thirteen tributaries were treated with the chemical lampricides 3-trifluoromethyl-4-nitrophenol (TFM) and Bayer 73 was used on five tributary deltas. The number of lamprey wounds per 100 fish has fluctuated through time (see figure) with rates presently greatly exceeding targets. The goal of the long-term control is to achieve wounding rates of less than 25 per 100 lake trout and 15 per 100 Atlantic salmon. In 2007 an improvement in wounding rates was observed: lake trout had an average of 46 wounds per 100 fish and salmon had an average of 71 wounds per 100 fish. Treatments in 2004 targeted several of the highest producing deltas and streams. Sea lamprey programs are cooperatively run by the US Fish and Wildlife Service, VT Fish and Wildlife Department and the NY State Department of Environmental Conservation.

Other non-chemical alternative sea lamprey controls that have been tested include: nest raking/disruption, sterile male release, trapping, and the installation of physical controls and low head barrier dams, including those on Lewis Creek in Vermont and the Great Chazy River in New York. A number of these alternative control methods show potential to reduce sea lamprey populations in the Lake.

More information is available in several LCBP technical reports about sea lamprey.

• Sea Lamprey Article & Graphics (LC Basin Atlas)
• Lake Champlain Sea Lamprey Control Page (www.champlainlamprey.org)

The tench (Tinca tinca), a fish originating from Germany, was first caught and identified by two fishermen on the Great Chazy in New York in May 2002. Brian Ellrott from UVM's Rubenstein Science Lab and Drew Price from the Center for Lake Champlain caught the 20- inch specimen near the lamprey barrier dam on the Chazy River.

Tench fish are native to Europe and similar to carp that live on lake or river bottoms. They are a slimy, slow moving carnivorous member of the minnow family that prefers tranquil, shallow water and weedy areas where they feed on invertebrates. It is unknown how the tench found its way to the Great Chazy, although the Richelieu River already has a viable tench population. In Europe, the tench is harvested and consumed by people.

It is too early to tell the effects of the tench on Lake Champlain's native species. Female tench may lay up to 600,000 eggs annually. The tench has a tendency to cloud the water where it lives by stirring up the bottom sediments. These fine sediments can suffocate the eggs and newly hatched fish of native species such as pike, perch or crappie.

• Tench Fact Sheet (Washington Department of Fish and Wildlife)
• Tench Fact Sheet (USGS)

Water Chestnut (Trapa natans)

European water chestnut (Trapa natans), first documented in Lake Champlain in the 1940s, displaces other aquatic plant species, is of little food value to wildlife, and forms dense mats that change habitat and interfere with recreational activities.

While there has not been a detailed survey of the extent of water chestnut in the Lake Champlain Basin, populations are established between Whitehall, New York and Ferrisburgh, Vermont, and in a few other waterbodies in the Basin.

The most extensive infestations are limited to southern Lake Champlain; several hundred acres are estimated to be infested. Mechanical harvesting and handpulling are the primary controls of the plant. It must be controlled each year before its seeds drop to the Lake bottom where the seeds can remain viable for up to twelve years. The South Lake infestation restricts boat traffic and other recreational uses, and water chestnut continues to require management in the Basin.

Since the 1960s, its local range has fluctuated in correspondence with management funding levels. It was nearly eradicated by the early 1970s, but lack of consistent control allowed water chestnut to expand its range. By 1997 it was found 52 miles north of Whitehall. An aggressive management program began in 1998 with an average annual budget of $500,000. Due to the program’s success, mechanical harvesting is now needed only as far north as Benson, VT. Remaining areas are managed by handpulling.

• Water Chestnut Article & Graphics (LC Basin Atlas)
• Water Chestnut Fact Sheet (Invasive Plant Atlas of New England)

White Perch (Morone americana) are a relatively new nonnative invasive species of increasing concern in the Lake. In 2003, Quebec researchers found that white perch far outnumber native perch in Missisquoi Bay and are now the Bay’s most abundant fish. They may displace native perch by feeding on their larvae and compete for zooplankton which can lead to an increase in algal growth. White perch are also known to prey on walleye eggs along with white crappy, which has contributed to the significant decline in the walleye population.

• White Perch Fact Sheet and links (Wisconsin Department of Natural Resources)

The zebra mussel (Dreissena polymorpha) is a small freshwater mollusk native to the Caspian and Black Sea regions of Eurasia. They are thought to have been transported to North America in the ballast tanks of ships. Since their arrival in the Great Lakes around 1986, the combined impacts of zebra mussels have resulted in millions of dollars of damage and lost revenues. Zebra mussels can clog residential, municipal and industrial water intake pipes, foul boat hulls and engines, cover recreational beaches and lake bottoms cutting the feet of swimmers, and obscure underwater and archeological artifacts. Zebra mussels take over spawning habitats for Lake Trout, Smelt, and other fish. They consume microscopic plants and animals in large quantities, in competition with juvenile fish and native mussels. This also has the effect of increasing water clarity, which has some benefits, but can aid the spread of invasive plants to deeper areas of the lake. Zebra mussels have begun to kill many of Lake Champlain's native mussels by attaching to their shells, preventing them from opening to feed and respire. Seven mussel species native only to the Basin are now severely threatened.

Adult zebra mussels have spread throughout nearly all of Lake Champlain since they were first found in 1993. Missisquoi Bay and the Northeast Arm are the only areas of the lake with few zebra mussels, where native mussel populations remain relatively intact. Unfortunately, during 1999, adult zebra mussels were also found near Lake George Village and in Lake Bomoseen, VT and zebra mussel veligers were found in Lakes Dunmore and Hortonia, VT.

Because no effective zebra mussel control methods exist, education efforts are focused on reducing and slowing their spread to other lakes. Management actions have focused on controlling the mussels' attachment to surfaces and water intake pipes and on preventing further spread. The impacts of zebra mussel infestations on the ecosystem and underwater cultural artifacts are also not well understood, but ongoing worldwide research may offer some understanding of possible effects.

• Zebra Mussel Articles and Maps (LC Basin Atlas)
• Zebra Mussel Monitoring Program Page
• Zebra Mussel & Quagga Mussel Fact Sheet #1
• Zebra Mussel Spread Fact Sheet - Lake Champlain Sea Grant (264 KB PDF)

Invasive variable-leaved watermilfoil (Myriophyllum heterophyllum) was confirmed in the southern end of Missisquoi Bay in Lake Champlain in September 2009. Like Eurasian watermilfoil, variable-leaved watermilfoil is an aggressive, rapidly-growing nonnative species. It can crowd out native aquatic plants and can impede boating, fishing and swimming. It spreads by stem pieces, roots, and seeds, and "hitchhiking" on boats and recreational equipment. For more information on variable-leaved watermilfoil and tips on how to identify it, visit the Vermont DEC website.

• Variable leaved watermilfoil sign (PDF)

Didymo was confirmed in the Lake Champlain Basin in both the Mad River in July 2008 and the Gihon River in June 2010 by VT Agency of Natural Resources staff. In June 2007, didymo was found in the upper reaches of the Connecticut River and soon after in the White River (VT ANR News Release). In August '07, a small infestation was reported in the lower Battenkill River (NYSDEC News Release).

Didymosphenia geminata, commonly referred to as "didymo" or "rock snot" is a freshwater algae that has invaded streams and rivers in parts of New Zealand. Native distribution of the species includes cool temperate regions of Northern Europe and Northern North America. While not much of a threat to Lake Champlain itself, didymo may pose a threat to rivers and streams because it can form dense mats on stream beds. Scientific studies conducted around the world have yet to show that didymo has significant impacts to salmon and trout, but a few studies have shown that didymo can locally alter macroinvertebrate species diversity at a bloom site. Didymo attaches to the streambed by a stalk. It has a rough texture similar to wet wool and mimics strands of toilet paper, as opposed to other algal species which feel more slimy.

Didymo can be accidentally spread by people using rivers, as its microscopic cells can cling to boats, waders, fishing gear, sandals, and anything else that comes in contact with water. Gear must be dried for a minimum of 48 hours or cleaned with a bleach solution to get rid of the algae. For more details on how to clean gear, please read the fact sheets below. If you think you see didymo contact the LCBP immediately!

• Vermont ANR Didymo information
• Vermont ANR News Release on Didymo (July 10, 2008)
• NYSDEC News Release on Didymo (August 7, 2007)
• Didymo Fact Sheet (US EPA)
• New Hampshire Didymo Information