Learning Objectives

By the end of this section, you should be able to:

  • Understand aquatic invasive species issues.
  • Grasp the impacts AIS have had in the Great Lakes.
  • Describe why it is important and how you can help prevent the introduction and spread of AIS.


Overview of the Issue

Free from natural predators, aquatic invasive species reproduce rapidly in their new homes and compete with native species for food and habitat. They disrupt the food web in several ways, including reducing food available for native species and preying directly upon native species. Invasive species are also called “biological pollutants.” They are costly to manage and have led to a severe loss of biodiversity in the Great Lakes region, nation and the world.

The story of invasive species in the Great Lakes has been a long and profound one. Non-native species — or plants and animals that are found outside their native geographic range — have been influencing life in Great Lakes waters from the mid-1800s, when the sea lamprey was first detected in Lake Ontario.


A variety of terms are used to describe species that adversely impact ecosystems. Below, several common terms are defined, and the distinctions between them are called out.

  • Nonindigenous or non-native species — Plants and animals living outside of the area where they evolved. A fraction of these species (about 10%) are considered invasive. Some non-native species that quickly became invasive include zebra and quagga mussels. In 1985, the zebra mussel was introduced into the Great Lakes. They quickly took over in several of the Great Lakes, drastically changing the ecosystems; they continue to spread to small lakes inland within the Great Lake region. In 2007, zebra mussels were discovered west of the Rocky Mountains.
  • Invasive species — Any non-native species or other viable biological material, including its seeds, eggs, or spores, intentionally or accidentally transported into an ecosystem beyond an organism’s historic range. A species is considered invasive when it reproduces and rapidly spreads into new locations and causes economic or environmental harm or harm to human health. The term “invasive” has become the standard term that is most descriptive of the impact of these species.
  • Aquatic invasive species (AIS) — These are species (e.g., fish, mollusks, and plants) that are considered harmful and difficult, if not impossible to control and found in or near the water. Sea lamprey, zebra mussels, Eurasian watermilfoil and purple loosestrife are all considered aquatic invasive species in the Great Lakes region. For more information, see the Great Lakes Aquatic Nonindigenous Species Information System (GLANSIS)
  • Aquatic nuisance species (ANS) — Species that threaten the diversity or abundance of native species, the ecological stability of infested waters, or any commercial, agricultural, aquacultural, or recreational activities dependent on such waters. Note: Some scientists and natural resource managers use the both nuisance and invasive terms to describe species that cause harm to humans, the economy, or the environment.

Aquatic Invasive Species Identification

Learning to identify fish, invertebrates (crustaceans), microscopic organisms, and aquatic plants is essential to controlling the spread of invasive species. The following is a selection of the top invaders in the Great Lakes region.

Fish Invertebrates
Microscopic organisms Aquatic Plants
Sea Lamprey Fishhook Waterflea Blue Green Algae Purple Loosestrife
Round Goby Spiny Water Flea Viral hemorrhagic septicemia (VHS) Eurasian Watermilfoil
Asian (Bighead, Silver) Carp* Rusty Crayfish Hemimysis Phragmites
Eurasian Ruffe Zebra Mussel Bacterial kidney disease (BKD) Hydrilla*
 Alewife Quagga Mussel    European Frogbit
* Species has not yet established a population in the Great Lakes.

A complete list of Aquatic Invasive Species on the Great Lakes Aquatic Nonindigenous Species Information System (GLANSIS) searchable database.

See: Full Flickr Photo slideshow with titles

Pathways of Aquatic Invasive Species

How do invasive species get from one place to another? AIS can spread through many pathways, called vectors, which are sometimes human-related. It is often impossible to pinpoint how exactly an organism was introduced. Some specific pathways include recreational boating, improper disposal, commercial shipping and commercial operations.

Natural resource managers have intentionally introduced non-native plant and animal species into ecosystems for a variety of reasons. For example, certain non-native species of salmon have been introduced into the Great Lakes to boost recreational fishing and to control other invasive species, and non-native beetles were introduced to control purple loosestrife, an invasive wetland plant. However, introductions of some non-native species have created complex management issues and some detrimental ecological consequences.

Recreational Boating

Various recreational activities have unintentionally contributed to the spread of AIS in the Great Lakes region and the country. The zebra mussel spread rapidly throughout the Great Lakes and major river systems because of its ability to drift in its larval state (veliger) and easily attach to boats. Zebra mussels and their veligers can stay alive for several days out of water.

Overland dispersal — taking a boat out of one body of water and traveling over land to another — has contributed to the spread of invasive plants and animals. Many small inland lakes in the Great Lakes region that are unconnected by waterways but accessed frequently by trailered boats have established populations of zebra mussels, Eurasian watermilfoil and other invasive species.

Transport on watercraft, fishing gear, and other recreational equipment is a common way invasive species have spread. What can marinas and boaters do to slow the spread of existing species and stop the infestation of new AIS? See: Section 2: Role of the Marina Operator in AIS Prevention.

Improper Disposal

Another key pathway for invasive species is through the improper disposal or intentional release of unused bait, unwanted pets and plants. This issue is gaining public attention, as it is becoming a growing problem around the world. Best practice for disposal: wrap unused bait in a sealed plastic bag and put in the trash; return unwanted pets to where they were purchased; and place non-native plants in a sealed plastic bag and place in the trash. Releasing exotic pets (e.g., reptiles) into the wild creates a public health risk, as well as potentially severe environmental and economic impacts.

Commercial Shipping

Many invasive species in the Great Lakes were inadvertently transported from in the ballast water of transoceanic ships, increasing the spread of non-native species and the infestation of aquatic invasive species across the globe. The U.S. EPA estimates that approximately 30 percent of non-native species entered the Great Lakes in the ballast tanks of ocean-going freighters. Ships enter the Great Lakes through the St. Lawrence Seaway, connecting the Atlantic Ocean to the Great Lakes. This system of canals and connecting waterways also opened the door for invasive species, like sea lamprey, to enter the Great Lakes. Sea lamprey, similar to other species, entered Lake Ontario and quickly spread to all the Great Lakes.

Today, the United States and Canada require that most ships entering the Great Lakes exchange their ballast water while still at sea to reduce transport and introduction of invasive species. Recently the U.S. Coast Guard reported that no unmanaged ballast water was discharged into the Great Lakes since 2009.

Commercial Operations-Accidental Spread

The escape of non-native species into local waterways is one of the concerns of aquaculture. Aquaculture refers to the breeding, rearing, and harvesting of plants and animals in all types of water environments, including tanks, ponds, rivers, lakes, and oceans. Similar to agriculture, aquaculture can take place in the natural environment or in a manmade environment.

Some non-native species have been accidentally introduced through aquaculture operations. For instance, silver and bighead carp were brought to the U.S. in the 1970s to improve water quality in aquaculture facilities. Resource managers believe that the carp entered the Mississippi River system by means of aquaculture ponds flooding in the 1990s. Although silver and bighead carp have spread throughout the Mississippi River, they have not yet been established in the Great Lakes.

Impacts of Aquatic Invasive Species

Invasive species have created tremendous problems for natural resources, the economy, and human health. In 1989, for example, zebra mussels clogged the intakes for the Detroit Edison power plant in Monroe, Mich., shutting down the plant for several days and forcing the city to order restaurants and bars to close, industry to voluntarily shut down and hospitals to use bottled water.

Invasive plants can have a profound bearing on recreational access to the water and the shore. Purple loosestrife, Phragmites (common reed), and Eurasian watermilfoil, have become established in many wetlands and inland lakes, resulting in a loss of native plants and the wildlife that depend upon them. Removal is difficult and often requires the intervention of a qualified state agency. For example, Phragmites typically grows an average 12-16 feet tall in dense, thick stands, can block views to the water and prevent people and animals from accessing the shoreline. Once established, Phragmites is very difficult to remove and drastic measures like widespread aerial application of herbicides, managed large-scale burning and controlled flooding typically have to be used to eradicate the population.

Current research has connected invasive mussels to an increase in frequency and intensity of harmful algal blooms. Zebra and quagga mussels feed on plankton — microscopic plants and animals suspended in the water column. By feeding on and removing large amounts of plankton, they allow more sunlight to reach deeper in the lake, encouraging plant growth. That plant growth can be harmful algae that are toxic to fish, birds and humans. When there is a large, quick growth of the harmful algae, it is called a harmful algal bloom or HAB. The mussels consume nontoxic green algae, removing competitors to the harmful algae. Also, mussels excrete the algae’s phosphorus, which acts as a fertilizer and contributes to increased harmful algal blooms.

Stop Aquatic Hitchhikers!Stop Aquatic Hitchhikers logo

Since aquatic invasive species were first established in the Great Lakes region, federal support to control invasive species was initially focused on the region. However, AIS have become a more widespread issue, with many reports of invaders spreading to ports and inland waterways throughout the country and different parts of the world.

With direction from the Aquatic Nuisance Species (ANS) Task Force, the USFWS and U.S. Coast Guard developed consistent messages, materials and guidelines to help stop the spread of invasive species throughout the nation. The Stop Aquatic Hitchhikers!TM campaign has more than 1,000 partners educating boaters, anglers, and other recreationists in the U.S. about how to prevent the spread of AIS, including aquatic plants, animals or microscopic organisms that can readily be transported to other waters via popular recreational activities.

For more information on this campaign, see: stopaquatichitchhikers.org

Next: Section 2: Role of the Marina Operator in AIS Prevention