• Zebra mussel (Dreissena polymorpha)
• Quaqqa mussel (Dreissena bugensis)
• Chinese mitten crab (Eriocheir sinensis)
• New Zealand mud snail (Potamopyrgus antipodarum)
• Asian clam (Corbicula fluminea)
• Rusty crayfish (Orconectes rusticus)

Eurasian water milfoil was first found in Connecticut in 1979 and can now be found in over 40 lakes and ponds in Connecticut as well as the Connecticut River. Eurasian water milfoil is a  rooted, annual plant with a tan or reddish stem, submerged leaves are usually in whorls of four around the stem. It spreads through primarily through fragmentation. When Eurasian water milfoil reaches the surface, it can form a dense mat, which interferes with boating, swimming and other recreational activities, and can alter the ecosystem of the lake. These plants also produce a reddish flower that emerges from the water.

Variable leaf milfoil was first discovered in Connecticut in 1936 and can now be found in approximately 30 lakes and ponds in Connecticut. Variable leaf milfoil is a rooted, annual plant with a thick red stem and has submerged leaves that are typically opposite. It spreads through fragmentation. Like Eurasian water milfoil, variable leaf milfoil can form a dense mat, which interferes with boating, swimming and other recreational activities, and can alter the ecosystem of the lake. These plants also produce flowering spikes that can emerge from the water.

Curly leaf pond weed is one of the most common invasive plants in Connecticut. It was first discovered in 1932 and can now found in 40 Lakes and pond in Connecticut as well as the Connecticut and Housatonic Rivers. Curly Leaf Pond Weed has a flattened stem with alternate leaves. The leaves are stalkless and have wavy edges (where it gets its name from). These plants spread via turions (soft, hardened leave). Like the invasive milfoil, curly pond weed can produce large, dense mats that interfere with water activities and can alter the ecosystem of the waterbody. These plants differ from most of the invasive plants in Connecticut, in that they often die back by mid-summer. The turions are dormant until the autumn when the water is cool.

photo credit: UCONN IPANE

Hydrilla was first discovered in 1989 and can now be found in two lakes in Connecticut, but is considered extremely aggressive and can outcompete native and invasive species. Hydrilla is a perennial with five whorled leaves which are finely toothed, around the stem. It spreads through fragmentation and tubers that overwinter in the sediment.

Fanwort was first discovered in 1937 and can now be found in more than 30 lakes in Connecticut and in wetlands along the Connecticut River. Fanwort has submerged leaves that are opposite and have petioles, or short stems. They also have a few small oval, floating leaves at the top of the plant just before the white or pickish flower that can emerge from the water. Fanwort spreads primarily through fragmentation.

Water chestnut was first discovered in Connecticut in 1999 and can be found in the following locations: scattered sites along the Connecticut River from Hartford to Lyme, both in the main stem river and in a number of coves (including White Oaks Cove, Keeney Cove, Hamburg Cove) and connected ponds. Water chestnut has also been found in a number of other waters scattered throughout CT including the Mattabesset, Hockanum and Podunk Rivers, small ponds in Eastford, Thompson and West Hartford, Bantam Lake (eradicated, non found in the last several years), Mudge Pond and at the confluence of the Still River and the Housatonic River.

Anglers fishing in the Connecticut River, its tributaries, and elsewhere should be on the lookout for this highly invasive plant. DEEP and other organizations are involved in eradication efforts.

Water chestnut is a rooted, annual aquatic plant with triangular-shaped floating and feather-like submerged leaves. Its sharp, spiny fruits wash ashore and can inflict painful wounds if stepped on. Dense water chestnut growth can make fishing, boating, swimming and other recreational activities nearly impossible. 

If you find this plant, contact Harry Yamalis at 860-424-3034 or harry.yamalis@ct.gov . 

Didymo (Didymosphenia geminata): a threat to trout streams. Your help is needed to prevent the spread of didymo. This highly invasive freshwater alga (also called "rock snot") has now been found in popular trout streams located a number of northeastern states (New Hampshire, Vermont, New York, Pennsylvania, Maryland, West Virginia and Virginia). Didymo has the potential to alter food webs and degrade habitat in many Connecticut trout streams.

Didymo is typically found in shallow streams with rocky substrate. Thought to be native to northern regions of Europe, Asia and North America, didymo originally was found only in cold, clear, low-nutrient waters.

Didymo's geographical and ecological ranges have been expanding, and now also include warmer and more nutrient-rich waters. The occurrence and intensity of blooms are also increasing. It is currently unclear why.

The microscopic didymo cell produces a stalk to attach to the substrate. During blooms, didymo can produce large amounts of this stalk material, forming thick mats of cottony material that feels like wet wool on the bottoms of rivers and streams. These mats can potentially smother aquatic plants, mollusks, destroy invertebrate and fish habitat, and impact existing food webs.

Anglers are considered an important vector responsible for the recent spread of didymo. The microscopic cells can cling to fishing gear, waders (felt soles can be especially problematic), boots and boats, and remain viable for months under even slightly moist conditions.

What you can do to prevent the spread of didymo:

Before leaving the launch:

• CLEAN: remove any visible mud, plants, fish or animals before transporting equipment.
• DRAIN: eliminate water from equipment, such as a live well, before transporting.

• DRY: anything that comes into contact with water (boats, trailers, anchors, propellers, fishing equipment, clothing, dogs, etc.) for a minimum of one week during hot/dry weather and four weeks during cool/wet weather.

• Wash with hot water (preferably high pressure).
• Dip equipment into 100% vinegar for 20 minutes prior to rinsing.
• Use a 1% salt solution (1oz. per gallon) or soap and hot water (Lysol, boat soap, etc.) for 10 minutes prior to rinsing.

Vermont DEC

Biosecurity - New Zealand

US EPA Region 8

Aquatic Invasive Species