Aquatic Invasive Species

What are Aquatic Invasive Species?
Aquatic Invasive Species (AIS) are invasive plants that live on, in or near water or invasive animals that require a watery habitat (USDA). Invasive species share the following characteristics:
1. They are not native to the ecosystem. Some species may be native to the United States, but not Wisconsin; some could even be native to one part of the state, but not another!
2. Invasive species cause economic and/or ecological harm (e.g. crowding out native species, clogging water intakes, reducing commercial catches, etc.)
3. They often spread quickly because of prolific reproduction and/or a lack of native predators; in their native habitats, invasive species probably have predators keeping their numbers in check, but in their invaded habitat, there's often nothing to eat them and stop their spread.

What Can You Do?
Learn about the invasive species in the areas where you boat/fish. Visit the municipal boat launches to see brochures and kiosks with more information. 

 Always follow the Wisconsin DNR's steps for preventing the spread of AIS:
  • Inspect boats, trailers, and equipment
  • Remove all attached aquatic plants and animals
  • Drain all water from boats, vehicles, and equipment
  • Never move plants or live fish away from a water body
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Watch out for...

Hydrilla and Brazilian WaterweedBrazilian Waterweed (Barry Rice,, Identification: Hydrilla has small, spiny leaves with pointed tips in whorls of 3-10 around the stem. It has spiny midribs on the underside of its leaves. It grow underwater and branches out close to the surface. Brazilian Waterweed has finely serrated leaves in whorls of 3-6. It can be distinguished from Hydrilla by the smooth midribs under its leaves.  (Photos: Barry Rice,, (USDA APHIS).

Curlyleaf Pondweed (Chris Evans, Illinois Wildlife Action Plan)

Curly-leaf pondweed Identification: It grow underwater with flower stalks above the surface. Leaves are translucent, 4-10 cm long with wavy, finely toothed edges. Impact: Curly-leaf pondweed outcompetes native species because it tolerates harsher conditions.
 (Chris Evans, Illinois Wildlife Action Plan,

Eurasian Water Milfoil
 Eurasian Water Milfoil (Barry Rice,,
Identification: It grows underwater, except for a flowering spike above the surface. Its leaves are in groups of four whorled around the stem and made up of smaller leaflets. Impact: It forms dense mats that shade out native species, hinder recreation, and clog pipes. (Barry Rice,,

Common Reed
: It can grow over 15 feet tall with green or tan stems and flat, greyish green leaves. Plumes at the top of the plant are dense and feathery.
Impact: It spreads rapidy and grows densely in wetlands and along shores, crowding out native species.
Phragmites (Jill Swearingen, USDI NPS,
(Jil Swearingen, USDI NPS,

Purple Loosestrife
 Identification: Stalks are woody and can grow over 6 feet tall, while leaves are downy with smooth edges. Flower spikes have small purple flowers with yellow centers. Impact: They produce millions of easily spread seeds each year, crowding out native plants and reducing wildlife food sources and habitat.
Purple Loosestrife (Norman Rees, USDA Agricultural Research Service,
(Norman Rees, USDA Agricultural Research Service,

Japanese Knotweed
Identification: Stems are reddish brown and resemble bamboo. Leaves are spade-shaped. Flowers are whitish green and are in clusters resembling plumes.

Impact: Japanese knotweed, while not an aquatic invasive species, invades riparian areas. It colonizes easily, leading to dense thickets that prevent native species from growing. Japanese knotweed also produces chemicals that are toxic to other plants.

(US Fish and Wildlife Service)

Zebra and Quagga Mussels
Identification: Both species have tan bodies with bands of color. Quagga mussels have a more rounded shape than zebra mussels, which are triangular. Zebra mussels have one flattened side, as well as thread-like attachements that help them attach to the substrate. Both can be as small as half an inch. Impact: Both species compete with fish for food, clog pipes, and alter ecosystems by increasing clarity of water.
Quagga Mussel (Amy Benson, USGS, Mussel (Amy Benson, USGS,
(Amy Benson, USGS,

New Zealand Mudsnails
Identification: They are typically around 5 mm in size. Their shells are light to dark brown with 5-8 whorls. Impact: New Zealand mudsnails are able to outcompete native species by surviving in many conditions, reproducing quickly, and competing for food and habitat.
Mudsnails (Mohammed El Damir,
(Mohammed El Damir, Pest Management,

Spiny and Fishhook Waterfleas
Identification: Spiny waterfleas' bodies are 1.5 cm in size. They have a pointed tail with spines. Fishhook waterfleas are 6-13 mm in size. They are transparent and have an angled tail with three barbs and a hook at the end. Impact: Both species compete with native fish for food. Spiny waterfleas can damage fishing equipment.
Spiny Waterflea (Jeff Gunderson, U of MN Sea Grant Program)
(Jeff Gunderson, Minnesota Sea Grant Program)

Freshwater Jellyfish
 Identification: They grow to be .5-2.5 cm. They are transparent and gelatinous with tentacles. Impact: Freshwater jellyfish compete with native species for food.

Rusty Crayfish
Identification: Rusty crayfish are larger than other crayfish species. They have a rust-colored spot on each side of their bodies and black bands on the tips of their claws. Impact: They displace native species through aggression and competition for food. They also destroy aquatic plants. Rusty Crayfish (USGS Archive, USGS,
(USGS Archive, USGS,

Red Swamp Crayfish
Identification: Adults have dark red bodies with long, narrow pincers and wedge-shaped black stripes on their abdomens. Juveniles have grey bodies. Impact: They compete with native crayfish species for food and habitat, spread diseases, and impact amphibian populations through predation and habitat competition.
Red Swamp Crayfish (Chris Taylor, IL History Survey,
(Chris Taylor, IL History Survey,

Round Goby

: Females and juvenile males are mottled grey and brown, while spawning males can be almost completely black. They have large, round heads and fused pelvic fin on their underside. They look similar to native sculpin.
Impact: Round gobies are very aggressive. They compete with native species for food and habitat.
RoundGoby (Center for Great Lakes and Aquatic Sciences Archive_UnivofMich_BugwoodDOTorg.jpg
(Center for Great Lakes and Aquatic Sciences Archive, University of Michigan,

Sea Lamprey

: They are eel-like and 12-20 inches long. Their backs are dark brown or black and their undersides are grey or pale brown. They have one long dorsal fin and a circular mouth with rows of teeth.
Impact: Sea lampreys attach to other fish and suck on blood and bodily fluids. A lamprey can eat more than 40 pounds of fish in its lifetime.
Sea Lamprey (Lee Emery, USFWS,
(Lee Emery, USFWS,

Viral Hemorrhagic Septicemia (VHS)

: Infected fish can have bulging, red-tinted eyes, bloated abdomens, open sores, and skin, gills, and fins that appear bruised.
Impact: VHS causes internal hemorrhaging and can be fatal to fish.
VHS (Dr. Mohamed Faisal, MSU)
(Dr. Mohamed Faisal, Michigan State University) Municipal Boat Launches

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Development of the municipal boat launch kiosks, AIS brochures, and this webpage were funded by the Wisconsin Coastal Management Program and the National Oceanic and Atmospheric Administration, Office of Ocean and Coastal Resource Management under the Coastal Zone Management Act, Grant #NA12NOs4190091.

Assistance with development of the informational materials was provided by Carrie Sanda, Douglas County AIS Coordinator.
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WCMP Color Title Logo.jpg