Know Your Aquatic Invasive Species

Know Your Aquatic Invasive Species

Aquatic invasive species refer to any non-native aquatic species that invades ecosystems beyond their natural, historic range. Also called called exotics, nonindigenous or non-natives, these troublesome invaders are spread sometimes intentionally through aquariums, or unintentionally by ships, boaters, hunters and other outdoor activities around water.

Aquatic invasive plants include algae, floating plants, submersed plants, and emergent plants. Aquatic invasive animals include insects, fish, reptiles, mollusks, crustaceans, and amphibians. Other aquatic invasive organisms include pathogens (disease-causing organisms), such as molds, fungi, bacteria, and viruses.

These organisms tend to be harmful in that they thrive in their new environments and crowd out resources needed for native species to survive. Controlling their spread is key, as many are basically impossible to eradicate. We can take measures to control them as eliminating them isn’t an option.

For our purposes we'll highlight just a few of each that are of most concern to those of us who enjoy the water for recreation.



These include plants that are rooted in the bottom with part or all of the plant underwater, as well as plants that float freely without contacting the bottom. 


Eurasion Watermilfoil - Deceptively delicate and fragile in appearance, the Eurasian watermilfoil forms thick mats in shallow areas of a lake, quickly growing and spreading to block sunlight, killing off native aquatic plants that fish and other underwater species rely on for food and shelter. In North America, the plant threatens the diversity and abundance of native plants, as well as the ecological balance of lakes and ponds.

This invasive perennial can grow up to 20 feet, which helps it crowd out other plant species, and then depletes oxygen once the thick mats die and begin to decay. You can easily spot it thanks to its long, stringy reddish stems that float near the surface.


Water Hyacinth - One of the fastest growing plants known; water hyacinths can double populations in two weeks. This is partly due to the fact that plants are capable of growing thousands of seeds each year, which remain viable for up to 30 years. Water hyacinth can also produce vegetatively by producing short runner stems.

Its thick, waxy leaves sprout from stems that can reach heights of up to one meter above the water, thus choking out most of the other vegetation. Today, water hyacinth occurs throughout the southeastern states, north to Virginia and west to Texas, and in California and Hawaii. SOURCE:

Hydrilla - this pest is considered one of the worst aquatic weeds in the United States. The plants have long stems (up to 30 feet in length) that branch at the surface and form dense mats. Hydrilla is named after Hydra, the 9‐headed serpent of Greek mythology, because it can grow an entirely new plant from a tiny stem fragment. It’s easy to imagine such fragments being stuck to any surface and potentially being transported to a new aquatic environment.

Currently, hydrilla has become established from Florida to Connecticut and west to California and Washington, with the most severe occurrences being found in the Gulf and South Atlantic States


Some of these infest waters or can attach to boats, while others can become tangled on propellers, anchor lines, or boat trailers.  Others can survive in bilge water, ballast tanks, and motors or may hide in dirt or sand that clings to nets, buckets, anchors, and waders.


Asian Carp - This family of leaping invasives has become one of the poster children of invasive species, as videos of infested waterways became viral over the years. They are fast-growing and prolific feeders that out-compete native fish and leave a trail of environmental destruction in their wake. They typically inhabit rivers, and bighead carp, black carp, grass carp, and silver carp that originated from Asia are collectively known as Asian carp.

These carp were imported into the country for use in aquaculture ponds. Through flooding and accidental releases, they found their way into the Mississippi River system, which is like a giant freshwater highway that has given invasive Asian carp access to many of the country’s rivers and streams.


Zebra Mussels - these are often found clustered around anything that has spent significant time underwater. They tend to clog up nets, moorings, motors and pipes to the point that they damage infrastructure and force out other species. Their larva are very small and often can’t be seen by the naked eye, making the transport of them extremely easy.

They have been discovered most recently in moss balls, which are plant products sold at aquarium and pet supply stores, garden centers, and florist shops. To effectively prevent them from spreading, follow the DESTROY, DISPOSE, DRAIN instructions. You can destroy them by boiling, freezing or using bleach, dispose of the moss ball and its packaging in a sealed container, or drain your aquarium and sterilize the contaminated water with 1/3 cup of bleach per gallon before dumping it down a drain.

Sea Lamprey - these parasitic fish are the worst of the alien species to invade the Great Lakes. Before control, sea lampreys destroyed many times the human fish catch. They are thought to have migrated from the Atlantic through the Erie canal.

They really are the stuff of horror films - it uses its suction cup-like mouth to attach itself to the skin of a fish and rasps away tissue with its sharp, probing tongue and keratinized teeth. A fluid produced in the lamprey's mouth prevents the victim's blood from clotting.

Thanks to the work of organizations like the Great Lakes Fishery Commission, lamprey numbers are largely under control in the great lakes from the near-record highs in 2017.


Spiny Water Flea - these are actually crustaceans, but are known as zooplankton – small animals that rely on water currents and wind to move long distances. They were transported from northern Europe in the ballast water of oceangoing ships. Today the spiny water flea is found in all of the Great Lakes and has begun to invade smaller inland waters of the Great Lake states and Canada.

They tend to feed on other zooplankton, and their long spines make them difficult to consume, leading to less food with lower nutritional value for native fish. Female spiny water fleas can produce up to 10 offspring every two weeks during the summer months. Their eggs can become dormant and survive the winter months on lake bottoms before coming to life in the spring.

ORGANISMS - often microscopic organisms can wreak havoc in the form of disease.

Whirling Disease - this is a disease of salmonid fish, the family of fish that includes trout, salmon, and whitefish. The disease is caused by an invasive parasite, which causes the fish to swim erratically (whirl) and have difficulty feeding and avoiding predators. Other physical signs of the disease include darkened tail, twisted spine, or deformed head. There is no known cure.

Viral Hemorrhagic Septicemia (VHS) is a deadly fish virus and an invasive species that is taking its toll on over 50 species of freshwater and marine fish. Living fish afflicted with VHS may appear listless or limp, hang just beneath the surface, or swim very abnormally. They will have darker coloration, often bulging eyes and bleeding around the eyes and gills.

The Type IV-b strain has been spreading among freshwater fish in the Great Lakes region since at least 2003, resulting in some massive die-offs since 2005 of many species in the affected lakes. The virus has been shown to survive two freeze/thaw cycles in a conventional freezer, suggesting both live and frozen bait could be responsible for  transmission.


As we explore the outdoors hunting or fishing, we need to be aware of the organisms that may 'come along' with us back home through our boot soles, insoles and especially waders

Take extra care in cleaning mud and organic matter off your gear before loading it into your vehicle. Be aware that there are organisms that can survive long after your trip, so clean your gear thoroughly after use as well.

Recreational boats are another way that unwanted species are moved between waters. Thousands of partners are working to help boaters and other recreational users understand the importance of “Clean Drain Dry” and how to avoid unintentionally spreading invasive species.


  • Boats, trailers, and gear
  • Remove all weeds, mud, and hitchhiking contaminants from axles, wheels, undercarriage, motor, prop, nets, and gear before leaving the boat landing


  • Water from boat, bilge, motor and livewell
  • Remove drain plug and open all water draining devices
  • Trash unused bait


  • Everything for at least five days before going to other waters
  • OR
  • Decontaminate with high pressure water (120F or warmer)

For more information, contact

While we may not be able to eradicate these invasive species, we can all do our part in the outdoors to stop the spread. It’s all part of enjoying the water we have for generations to come.   -WR

Back to blog

Suggested Products