Aquatic Invasive Species

Over the past 200 years, 180 non-native species have found their way into the Great Lakes

The construction of the St. Lawrence Seaway in the middle of the 20th century led to unprecedented invasions of aquatic non-native species that caused and continue to cause great harm to the native species. The lengthy cycle of low water from 2000-2013 also led to the infestation of Great Lakes shorelines by exotic flora, the most recent of which is phragmites australis.

Georgian Bay Great Lakes Foundation strives to inform the public and educate governments about the seriousness of such threats as Asian Carp and the latest information on possibilities to control them.

Grass Carp – an invasive species that could harm Georgian Bay’s wetlands and destroy fish spawning sites

Non-native species introductions are not new to the Great Lakes. Over the past 200 years, 180 non-native species have found their way into them. Twenty-five of these are fish species. The vast majority of introductions are a result of direct human activities such as building the Erie and Welland canals, release of ballast wastewater from ocean going freighters or direct stocking of non-native species such as rainbow trout, brown trout and several Pacific salmon species. Some of the introductions have not had overt negative impacts but there are many that have and these are referred to as invasive species. The earliest of the invasive species into the Great Lakes include sea lamprey. Government agencies in Canada and the US spend millions annually on chemicals to try to keep sea lamprey under control.

More recently, invasive species have become an even greater concern for scientists and the public. Some species are having a direct impact on the food chain and ecosystem. These species are typically the filter feeders of microscopic life such as phytoplankton (plants) and zooplankton (animals). This includes the zebra and quagga mussels, and spiny water flea. Their colonization within the Great Lakes has caused the aquatic ecosystem to move away from a rhythmic balance that maintained itself in a relative constant equilibrium to one that has become chaotic in nature. This drastic upheaval is especially true and ongoing in all of the Great Lakes except Lake Superior.

In 2019, Georgian Bay Great Lakes Foundation assisted the Tiny Township Council in developing a resolution which was adopted by the Great Lakes and St. Lawrence Cities Initiative. It strongly urges that Grass Carp be totally eradicated in the Great Lakes and connecting rivers in Ohio.

Asian Carp

And now new threats, the Asian Carp characterized by four species (Grass, Bighead, Silver, and Black) sit on the Great Lakes doorstep in the Chicago shipping canal. These species are particularly dangerous to the Great Lakes because of their ability to consume the food base that native fish species require, or to rip apart Georgian Bay’s high quality wetlands. This characteristic coupled with their ability to grow and reproduce quickly adds to the threat. One species, the Silver carp in particular, adds another threat by jumping out of the water as it reacts to boat motor noise. Their natural avoidance reaction is a potential danger to boaters.

Until recently the greatest concern has been the Bighead and Silver carps. In parts of the Mississippi drainage system the Bighead and Silver carp, being non -native species, now represent more than 90% of the fish biomass owing to their aggressive feeding nature and their ability to easily colonize the existing environment and reproduce rapidly.

If Asian Carp find entry into the Great Lakes and conditions are right for their colonization, the combined impact with zebra and quagga mussels will surely spell an increased threat to some native species that occupy the near-shore habitats in Lakes Michigan, Huron, St. Clair, Erie and Ontario. Lake Superior may be spared due to its cold temperatures.

Grass Carp

Another species, the Grass carp, was first introduced into the United States (Arkansas and Alabama) in 1963 to a U. S. fisheries research station. They were introduced as a biological plant control in ponds. The species has a voracious appetite for aquatic plants. It was thought that the species would likely not reproduce because they required moving water (rivers) to reproduce, and stocking would be permitted only in ponds.

Unfortunately, in 1966 there was an accidental escape from a U. S. government facility. Since then, there have been widespread authorized, illegal, and accidental introductions throughout the U. S. By the 1970s the species was reported in 40 states and now is reported present in 45 of the United States’ 50 states.

Grass Carp Biology

Grass carp grow very rapidly. Young fish stocked in the spring at 20 cm (7.9 in) can grow to over 45 cm (18 in) by fall. Their maximum length is 1.4 m (4.6 ft) with a maximum weight of 40 kg (88 lbs). They normally live about 11 years but a lake in Washington State has recorded some fish that are 15 years of age. They eat up to three times their body weight each day.

They thrive in lakes, ponds and backwaters of large rivers that provide an abundant supply of freshwater vegetation as food.

Spawning occurs during the summer months in fast-moving rivers during high flows.

The principal issue with Grass Carp is their ability to colonize habitat that is occupied by native species. Their sheer numbers simply out-compete native species for space and food and destroy habitat that is occupied by young native fish species. In addition, they are capable of destroying spawning habitat directly as a result of their relentless ability to consume vegetation. This would include but not be limited to destruction of spawning habitat for species such as yellow perch, northern pike and muskellunge, largemouth bass, sunfish and rock bass.

Grass Carp, with their voracious appetites, also pose a serious threat to waterfowl habitat and wetlands.

If Grass Carp gain access into the Great Lakes, the more productive southern warmer waters will likely be most impacted by their colonization. Colonization will occur via the near-shore waters and therefore take some time to complete. The most threatened of areas will be the shallow, well-vegetated areas and include the extensive coastal wetland areas.

In Georgian Bay, it appears that the most vulnerable area for colonization is the area of Severn Sound, owing to its shallow nature and abundance of plant life. However, near-shore waters as far as Sault Ste. Marie would see colonization, but perhaps at fewer numbers, because the more northern waters of Georgian Bay tend to be more oligotrophic; i.e., have fewer nutrients.

It is currently estimated that, unless Grass Carp are eradicated immediately, they will quickly colonize the middle and lower Great Lakes and destroy the wetlands.

Grass Carp for Sale

In the United States seven states (Colorado, Nebraska, Iowa, Missouri, Arkansas, Mississippi, and Alabama) sell Grass Carp that can reproduce. These fish are fertile and are called diploid carp. There are a number of states along the U.S./Canada border that do not allow the purchase or stocking of Grass Carp and other Asian Carp species. About thirty-one states allow the purchase of triploid Grass Carp. Triploid Carp are fish that are produced from fertilized eggs that have been pressure treated. Pressure treating eggs results in sterilization of the developing embryo and fish.

Naturally reproducing populations have been established in a number of states in the Mississippi basin. In 2013, the United States Geologic Survey found four Grass Carp in the Sandusky River, Ohio. In 2015, a graduate student with the University of Toledo found eight Grass Carp eggs in the Sandusky River. Fertilized Grass Carp eggs remain in suspension as the drift downstream in a river. Based on drift egg dispersal pattern, there were probably many more than eight eggs that were deposited. The likelihood of Grass Carp colonizing the Sandusky River and the Maumee River is rapidly increasing with time. Grass Carp have also been captured in the St. Clair River and Lake Huron.


The Georgian Bay Great Lakes Foundation recommends the prohibition of the production, sale, live shipment, stocking, import and export of Grass Carp for all U.S. states that border the Great Lakes. Ontario and our Federal Government prohibit the importation and or sale of any live Asian Carp. Instead, these Asian Carp species must be eviscerated and have their heads cut off so they are clearly dead when they cross the border.

It is extremely difficult to control the spread of an invasive species once it is established, which makes prevention the most cost-effective approach in dealing with organisms that have not yet entered or become established in the Great Lakes.

What you can do!

If you see or catch a suspected Asian Carp of any type (e.g. Grass Carp), please report it immediately on the Invading Species Hotline at 1-800-563-7711.

And learn the actions that you can take.