Appearance: Carolina fanwort is a perennial aquatic plant with fan-shaped underwater leaves and small, notched floating leaves. It blooms solitary white to purplish flowers above water from late June to September in Michigan. Fruits are less than 7 mm and have three seeds.²

Threats: Stems are typically under 10 feet long but can grow up to 33 feet mats that reduce oxygen, alter pH, and choke out native vegetation.³

Great Lakes Region: Minimal in Michigan, Illinois, Indiana, Ohio, Pennsylvania and New York

Appearance: Eurasian watermilfoil is a submerged plant with feather-like whorled green leaves and reddish stems. It produces pink flower spikes with tiny yellow flowers. ⁶

Threat: Eurasian watermilfoil forms dense mats, spreads rapidly, blocks sunlight, and crowds out native plants vital for fish and wildlife.⁷

Great Lakes Region: Michigan, Ohio, Indiana, Illinois, Wisconsin, Pennsylvania

Appearance: This submersed perennial herb is rooted, with long stems that branch at the surface to form dense horizontal mats. Its small, pointed leaves grow in whorls of 4 to 8, have serrated edges, and may feature sharp teeth under the midrib.¹⁰

Threat: Hydrilla threatens native aquatic ecosystems by forming dense mats that block sunlight, disrupt native plants, and change the water’s ecology. Its invasion also hampers boating and fishing activities.¹¹

Great Lakes Region: Mostly Pennsylvania; Minimal in Michigan, Ohio (southern), Illinois, Wisconsin, New York ¹²

Appearance: Parrot Feather grows in lakes and wetlands in sun or shade and is recognizable by its gray-green color with stems that may appear reddish up close. Though mostly submerged, its emergent stem tips show feathery, tightly whorled leaves.¹⁶

Threat: Thick parrot feather infestations create mosquito breeding habitat and degrade water quality as well as conditions for fish and other wildlife.¹⁷

Great Lakes Region: Minimal in New York, Indiana, Pennsylvania, Illinois and Wisconsin. Confirmed in Michigan and successfully eradicated.¹⁸

Appearance: Floating leaves are triangular to diamond-shaped with toothed edges, forming surface rosettes; stems are long, spongy, buoyant, and up to 16 ft. Small white four-petaled flowers bloom in mid-summer, and dark horned nuts develop underwater.²²

Threats: Dense mats of vegetation block sunlight and suppress native plants, can deplete dissolved oxygen during decomposition (harming aquatic life and causing fish kills), create hazards for boating, fishing, and swimming, and rapidly outcompete native plants, disrupting ecosystems.²³

Spread: Each plant produces up to 20 nuts (drupes) which contains one seed. Each seed can last up to 9 years in the soil before germinating, while most germinate within 2 years. Can spread by vegetation fragments as well.²⁴

Great Lakes Region: New York, Pennsylvania²⁵

Appearance: Upright purple flowers in clusters with free-floating rosettes and round waxy leaves.

Threats: Chokes waterways, reducing dissolved oxygen (leading to fish kills), impeding recreational boating and fishing, and damaging water infrastructure.²⁹

Spread: Each plant produces up to 20 nuts (drupes) which contains one seed. Each seed can last up to 9 years in the soil before germinating, while most germinate within 2 years. Can spread by vegetation fragments as well.

Great Lakes Regions: Michigan, Ohio, Indiana, Illinois, Wisconsin, New York, Pennsylvania

Appearance: Stiff sharp serrated leaves that appear to be aloe or pineapples with small white flowers.

Threats: Forms dense mats that crowd out native species and reduce biodiversity. It may alter water chemistry and harm aquatic organisms, while also impeding recreation; its sharp edges can cut swimmers.³²

Great Lakes Regions: None. Currently located in Ontario along the border of Lake Erie and Lake Ontario.