Aquatic Invasive Species

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

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.

What happened to this 2021 Grass Carp removal plan for Lake Erie?

Asian Carp Regional Coordinating Committee Releases 2021 Asian Carp Action Plan

March 22, 2021

Continued efforts led by Ohio and Michigan Departments of Natural Resources, with the U.S. Fish and Wildlife Service and other partners, to remove grass carp in Lake Erie. Additionally, the Great Lakes Fishery Commission and Ohio Department of Natural Resources will complete the evaluation of a seasonal barrier for grass carp in the Sandusky River.

Invasive Species on 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.

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

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.

Asian Carp, U.S. Fish and Wildlife Service Headquarters, Public domain, via Wikimedia Commons

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 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.

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.

Historical Perspective

Asian carp establish ‘finholds’ in Lake Erie, Ontario and Michigan

By Warren Schlote -August 29, 2018, The Manitoulin Expositor

Prediction is that invasive species will be established in Lake Huron within a decade

GREAT LAKES—Invasive grass carp pose a major threat to the Great Lakes basin; with experts warning the species will become established in Lake Huron in 10 years, opinions are strongly divided as to the best ways to deal with the threat, as well as the tactics agencies are using to manage these fish that belong to the Asian carp family.

Mary Muter, chair of the Georgian Bay Great Lakes Foundation, raises strong concerns in a press release her organization had published on July 25. She criticizes the Ohio and Michigan Departments of Natural Resources (DNRs) for their ongoing efforts to catch Lake Erie grass carp, implant them with tagging devices and release them to study their movements and better understand their patterns.

Instead, she says all agencies in the Great Lakes region need to begin eradicating the fish immediately.

Michigan has been a leader in the efforts to tag and study grass carp under direction of the Lake Erie Great Lakes Commission, a group that consists of representatives from provincial- and state-level environment management organizations. This includes the Ontario Ministry of Natural Resources and Forestry (MNRF), the Pennsylvania Fish and Boat Commission, New York State Department of Environmental Conservation, and the Ohio and Michigan DNRs.

According to Seth Herbst, aquatic invasive species coordinator at the Michigan DNR, the agencies in western Lake Erie have been able to use tagging studies to determine fish movement patterns and what habitats they prefer. “We’ve been using that to inform where and when we use our response actions, Mr. Herbst said, adding that they are completing some eradication efforts while conducting these studies.

An invasive species

Grass carp are native to eastern Asia, with a range from Vietnam to the Amur River near Siberia. They are an herbivorous fish, eating aquatic vegetation in mass quantities. Their voracious appetite is why people began to import them to North America, and is the same factor that makes them such a threat.

Pond owners have been stocking grass carp since the 1960s to manage their weeds without having to use pesticides. Grass carp eat vegetation from the top down, rather than ripping the roots out and increasing the water’s cloudiness.

Grass carp are one of four subspecies of the Asian carp family that also includes bighead, black and silver carp. All four are considered invasive species in North America. Grass carp are considered established in the Mississippi River drainage basin, and studies from the past decade have confirmed new fish are now spawning in the Great Lakes basin. Many of those fish have been traced to the Sandusky River in Ohio.

Two types of the same fish

Grass carp had proven themselves to be an excellent way of dealing with nuisance weeds, but sometimes, they were too good to be true. In Texas, officials stocked 270,000 grass carp into Lake Conroe in the early 1980s. After one year, the lake had lost 3,600 hectares of underwater vegetation and close to half of the native fish species had experienced declines. Some states have placed bans on fertile grass carp for this reason, a decision that had major impacts on pond owners who once relied on the fish.

Researchers found an alternative in 1983: If they gave the eggs a shock of either temperature or pressure at a specific time in the development cycle, the fish would keep an extra, third DNA chromosome that is normally discarded. That variation made them effectively sterile, as they would not be able to pass on the proper two-chromosome genes to future offspring. Those fish are referred to as triploid (three chromosomes) and diploid (two chromosomes) by biologists to represent their ability to reproduce.

Although success rates are close to 100 percent, the process is not perfect. Sometimes, best efforts to produce a batch of triploid fish may still result in some diploid individuals slipping through. Producers have to test every fish and the U.S. Fish and Wildlife Service samples 120 fish from each batch before certifying them as triploid, but there is still a small possibility that a presumed triploid fish could turn out to be fertile.

Currently, many states such as Ohio only allow triploid grass carp for vegetation maintenance, while other regions like Michigan and Ontario have outright bans on all grass carp. There are, however, seven states in the continental U.S. that still allow diploids: Alabama, Arkansas, Iowa, Mississippi, Missouri, Nebraska, and the portion of Colorado east of the continental divide.

State of the union

Approximately 12 grass carp have been captured in the Canadian waters of Lake Huron since the late 1980s. Since DFO started its Asian Carp Program in 2012, only two fish have been caught. Both turned out to be triploid.

“It’s a species that we’re concerned about and we go in with the intention of capturing these species in our early detection locations and removing them from the Canadian waters of the Great Lakes,” says David Marson, senior biologist and field operations lead of Fisheries and Oceans Canada (DFO)’s Asian Carp Program.

Grass carp are not likely to reproduce in Lake Huron for the next five years because of their low populations, as stated in a DFO risk assessment from 2017. However, that same risk assessment states that the numerous wetlands and tributaries around Lake Huron—especially Georgian Bay—would be prime habitat in which grass carp could live and breed. The risk assessment also says if existing Asian carp populations grow, the risk level for Huron and the other Great Lakes would increase considerably.

A population of reproducing grass carp now exists in Lake Erie and is poised to continue growing. Studies have predicted and later confirmed that grass carp spawn in Ohio’s Sandusky River, confirmed both by the capture of grass carp eggs in the river and from chemical analysis of mature fish that matched the compounds in the river.

The responsibility to conduct efforts to control and eliminate grass carp within U.S. waters falls to the state level. Higher-up agencies such as the Fish and Wildlife Service and the United States Geological Survey (USGS) help to coordinate a broader, unified effort and provide scientific backing, but the actual work is done by state agencies.

Waterways like the Sandusky and Maumee Rivers in Ohio and the warm water discharge from a power plant in Monroe, Michigan are proven hotspots for these fish, based on previous capture and study work. And while every agency in the Great Lakes basin has a role to play in managing Asian carp populations, because these fish tend to thrive in the western basin of Lake Erie, the response by Ohio and Michigan will play a major role in determining the future of the Great Lakes as a whole. That view is shared by DFO, Ms. Muter and researcher Nick Mandrak at the University of Toronto.

What’s at stake?

The most direct impact of grass carp is an environmental and ecological risk. According to a 2017 report, an average 15-year-old grass carp can eat between 60 and 200 kg of vegetation per year. That same study’s simulated models showed invaded wetlands lost over half their vegetation after just one year.

Wetlands are key to managing water quality by filtering out pollutants and providing opportunities for animal life to thrive. Wetlands are already under threat from invasive plant species, such as the phragmites infiltration on which The Expositor has previously reported—phragmites appears to be one of the few aquatic plants that grass carp do not eagerly eat.

Wetland loss also directly impacts fish populations, as wetlands provide numerous fish species with spawning grounds, food and cover from predators. As habitats are destroyed and available food becomes increasingly scarce, populations of native species would begin to decline.

That has economic impacts, too. If fish stocks decrease, Canada’s fishery industry stands to lose a great deal. As of 2018, commercial and recreational fishing, wildlife viewing and lakefront use total more than $1.2 billion in economic activity. That number could reach nearly $30 billion in 20 years, according to a DFO report.

Managing established invasive species is both challenging and expensive. Canada alone had spent $8.1 million on its sea lamprey program in 2016-2017, an invasive species that is established throughout the Great Lakes.

“Do we want another sea lamprey program, which costs $20-30 million a year to control them? That’s where we’re heading if we don’t act soon,” says Mr. Mandrak.

This is the first part of a series on grass carp in the Great Lakes. If you would like to learn more about Asian carp and the work being done to manage and understand them, visit or See our website at for further coverage.


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.