Aquatic invasive species (AIS) are non-indigenous species that dwell in water or wetlands whose introduction causes or is likely to cause economic or environmental harm or harm to human health. When AIS arrive in Polk County they have a competitive advantage over native species because they lack natural predators, parasites, pathogens, diseases, and competitors to keep their populations in check. As a result, populations of AIS can explode and outcompete native species by using available resources.
Additionally, many AIS have life strategies which give them a competitive advantage over native species. Strategies include high reproductive rates, early seasonal growth and development, and tolerance for a wide range of environmental conditions.
Invasive species can come from other parts of the United States or from other countries and can be released either intentionally or unintentionally. Modes and reasons for introduction can vary widely and include: ballast water for shipping, food sources, bait sources, and the garden/aquarium plant trade. Although some species may have been introduced through natural migration, humans are the primary way invasive species are spread.
AIS can displace native species; reduce wildlife habitat; and negatively impact property values, recreational activities, tourism, and industries.
In 2001, the Wisconsin Legislature directed the Department of Natural Resources to establish a statewide program to control invasive species and to promulgate rules to identify, classify and control invasive species for purposes of the program. By 2004, the Wisconsin Council on Invasive Species formed to assist DNR with this task.
As a result, on September 1, 2009 the DNR created Wisconsin’s Invasive Species Identification, Classification and Control Rule, Chapter NR 40, Wisconsin Administrative Code. The rule helps citizens learn to identify and minimize the spread of plants, animals and diseases that can invade our lands and waters and cause significant damage.
The invasive species rule creates a comprehensive, science-based system with criteria to classify invasive species into two categories: prohibited and restricted. With certain exceptions, the transport, possession, transfer and introduction of prohibited species is banned. Restricted species are also subject to a ban on transport, transfer, and introduction, although possession is allowed, with the exception of fish and crayfish.
Wisconsin has various laws in place to prevent the introduction and control the spread of AIS and diseases in Wisconsin.
- INSPECT your boat, trailer and equipment.
- REMOVE any attached aquatic plants or animals (before launching, after loading and before transporting on a public highway).
- DRAIN all water from boats, motors and all equipment.
- NEVER MOVE live fish away from a waterbody.
- DISPOSE of unwanted bait in the trash.
- BUY minnows from a Wisconsin bait dealer. You may take leftover minnows away from any state water and use them again on that same water. You may use leftover minnows on other waters only if no lake or river water, or other fish were added to their container.
In 2008 the Polk Countywide Illegal Transport of Aquatic Plants and Invasive Animals Ordinance was adopted, making it illegal to operate or transport equipment with aquatic plants or invasive animals attached. Public input into the decision making process was sought through public meetings which were advertised in local papers. The Ordinance was amended in 2011 to include language regarding liability of a vehicle, watercraft, trailer, or equipment of the owner or lessor.
The methods Polk County organizations use to fight aquatic invasive species are education, monitoring, and rapid response to an invader. Education occurs through newsletters, websites, presentations at meetings, and meeting watercraft users at boat landings. Many organizations participate in the DNR Clean Boats – Clean Water program to inspect watercraft before they enter County lakes. Several organizations perform aquatic plant surveys and/or underwater inspections to try to detect invasive species before they become widespread. Comprehensive point intercept aquatic plant surveys are also common every few years. Where aquatic invasive species are present, aquatic plant management plans are written so that the organization can work together with the DNR to control the invasive species.
To date there are documented populations of seven different AIS in Polk County: banded mystery snails, Chinese mystery snails, curly leaf pondweed, Eurasian water milfoil, Japanese/giant knotweed, purple loosestrife, and rusty crayfish. Additionally, zebra mussels are present just south of Polk County in St. Croix County.
The most common AIS in Polk County are curly leaf pondweed and Chinese mystery snails which are documented on 39 and 36 waterbodies, respectively. Banded mystery snails have been documented on 12 waterbodies, rusty crayfish on 10 waterbodies, purple loosestrife on 8 waterbodies, Eurasian water milfoil on 4 waterbodies, and Japanese/giant knotweed on 7 waterbodies.
Banded mystery snails are native to the southeastern United States, being found primarily in the Mississippi River System up to Illinois. This invasive snail species is popular in the aquarium trade which likely explains it’s presence outside its native range.
Besides causing aesthetic problems, banded mystery snails can cause mortality of largemouth bass embryos if nests are invaded. The banded mystery snail is easily distinguished by the presence of reddish bands which are arranged parallel to the whorl of the shell.
Banded mystery snails were first documented in Polk County in 2003 in Half Moon Lake. Although their spread had continued, they are still much less common in Polk County as compared with the Chinese mystery snail. They have been documented on only 12 Polk County waterbodies.
Chinese mystery snails were imported to the west coast in the late 1800’s as a food source for the Asian market and have spread via aquarium release and other accidental and intentional introductions. When introduced to a new water body, the Chinese mystery snail alters the ecosystem composition, structure, and function by competing with native snails for food and space.
Populations of Chinese mystery snails are established in many Northern Wisconsin lakes and have been documented in 36 Polk County waterbodies.
Curly leaf pondweed is a submerged aquatic invasive plant that is native to Eurasia, Africa, and Australia. It was accidentally introduced to the United States in the mid-1800’s by hobbyists who used it as an aquarium plant.
The leaves of curly leaf pondweed are easily distinguished by their rounded tip, prominent mid-vein, and finely toothed edges. In certain growing conditions, the leaves appear wavy or crimped. The leaves are reddish-green, oblong, and about 3 inches long.
Curly leaf pondweed is found in a wide variety of habitats, although it prefers alkaline and high nutrient waterbodies and typically grows in less than 3 meters of water.
This invasive species outcompetes native aquatic plants because it exhibits rapid growth in the early spring, sometimes growing beneath ice cover. Curly leaf pondweed forms large, dense mats on the surface of waterbodies inhibiting the light necessary for native plant growth and interfering with navigation and recreational activities. The plant usually drops to the lake bottom by early July.
Curly leaf pondweed was first discovered in Polk County in the Apple River Flowage in 1977. It has been documented in 39 waterbodies in Polk County.
Eurasian water milfoil is a submerged aquatic invasive plant native to Europe, Asia, and northern Africa. Eurasian water milfoil was first discovered in North America in the 1940’s. It first arrived in southern Wisconsin in the 1960’s and began to move to the northern half of the state in the 1980’s. Eurasian water milfoil spreads when small fragments of the plant break off, form new plants, and float on water currents or are transported by boater traffic.
Eurasian water milfoil is the only non-native milfoil in Wisconsin. All milfoils have four delicate, feather-like leaves arranged in a whorl around the stem of the plant. Eurasian water milfoil can be distinguished from native milfoils by the 12-21 leaflets making up each leaf.
Eurasian water milfoil is capable of forming large, thick mats which interfere with recreational uses. It can have devastating effects on native ecosystems, displacing native aquatic plants and impacting fish and wildlife populations.
Establishment of Eurasian water milfoil populations in Polk County has occurred relatively recently being first found in Long Trade Lake in 1995. Long Trade Lake is part of the Trade River System, which includes Little Trade, Big Trade, and Round Lakes in Burnett County. Eurasian water milfoil was discovered in Round Lake in 2003 and in Little Trade Lake in 2009. Eurasian water milfoil was found in Horseshoe Lake in 2006, in Pike Lake in 2010, in the St. Croix River between Spanglers Landing and Lions Park Landing in 2013, and in Cedar Lake in 2015. Eurasian water milfoil is currently documented on 5 Polk County waterbodies.
Japanese and giant knotweed are native to Asia and were imported to the United States in the mid 1900’s as ornamental plants, although they are becoming more prevenlant in the wild. The plant can reach up to fifteen feet and is easily distinguished by hollow bamboo-like stalks.
Knotweed is a perennial, meaning that each spring it re-grows from an extensive root system. Both species grow extremely fast and form a dense canopy of foliage which blocks sunlight from reaching the ground. As a result, native vegetation is unable to grow beneath a knotweed stand. When knotweed establishes on stream banks, the lack of understory can promote intense erosion causing soil and knotweed roots to move downstream.
Knotweed was first discovered in Polk County in 2009. In 2012 and 2013 knotweed control measures were conducted by LWRD under an early detection and response grant. Knotweed has been documented at 93 sites in Polk County and on 7 waterbodies.
Purple loosestrife is an aquatic invasive perennial plant that grows 3-7 feet tall and develops a spike of small purple flowers in late summer. Flowers are typically in bloom from July to September, with seed set beginning in mid-July. The leaves are oblong and arranged oppositely along a square shaped stem. The stem of this plant becomes woody with age and persist throughout the winter. Purple loosestrife spreads rapidly and colonizes wetlands, shorelines, and roadside ditches. Thick stands of purple loosestrife crowd out native vegetation and reduce food, shelter, and nesting sites for a variety of wildlife.
Through Wisconsin’s Purple Loosestrife Biocontrol Program, beetles which feed primarily on purple loosestrife have been introduced from Europe to wetlands in Wisconsin infested with purple loosestrife. Although there are many methods to control purple loosestrife (hand pulling, herbicide, etc) biocontrol may be the most viable long term control option. For more information on biocontrol or to participate in a biocontrol project, contact the Polk County Land and Water Resources Department or WDNR.
This plant, native to Europe and Asia, was introduced in North America in the 1800’s for beekeeping and as a garden ornamental. Purple loosestrife has been present in Polk County for many years. An inventory was conducted in 2000 by Polk County LWRD to identify the extent of purple loosestrife and to reduce its spread. Purple loosestrife is currently documented on 8 Polk County waterbodies.
Rusty crayfish are invasive crustaceans native to streams in the Ohio River Basin states of Ohio, Kentucky, Illinois, Indiana, and Tennessee. They were likely introduced to Wisconsin waters by anglers who used them as live bait. Rusty crayfish can be identified by the rust colored spots on the hard part of their upper shell.
Rusty crayfish can have profound impacts on lakes, rivers, and streams. They are more aggressive than native crayfish and are better able to avoid predation than native crayfish. They can also harm native fish populations by eating their eggs and young.
Rusty crayfish are currently documented on 10 Polk County waterbodies.
Zebra mussels are invasive mussels with a D-shaped shell exhibiting alternating black and white stripes. Since they are able to attach to hard surfaces, zebra mussels can clog water intakes and damage equipment such as boat motors. When water bodies are infested with zebra mussels their shorelines become littered with sharp shells, impeding human recreational opportunities. Zebra mussels are filter feeders that quickly remove plankton from water, disturbing the food web for small fish and native mussels. Their filtering action often makes water clearer allowing aquatic plants to grow in deeper water and spread to larger areas. Additionally, zebra mussels damage ecosystems by harming fisheries and smothering native mussels, snails, and crayfish.
Zebra mussels are native to freshwater rivers and lakes in Eastern Europe and Western Asia and arrived in the Great Lakes in the late 1980’s from contaminated ballast water. Since that time they have expanded in range via the Mississippi River. In September 2016, a single adult zebra mussel was found on the northeast side of Deer Lake by a citizen.