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  • Writer's pictureNew Wave Fishing Academy

Invasive Species: Grass Carp

Updated: Oct 29, 2023

Invasive species have the potential to completely flip an ecosystem upside down. In our mind the water bodies in Ontario are our crown jewel and we want to do our part to ensure they remain a prized resource. Over the course of 2023 New Wave Fishing Academy & the Invasive Species Centre will collaborate on preparing content to educate anglers on the 4 asian carp species that are threatening our waterways. We will cover why they are a threat to the Canadian waters of the Great Lakes, why anglers play an important role in monitoring for them, and what they can do to help stop the spread!

Asian carps were introduced to North America in the 1970s for use as biological control in aquaculture facilities. As these fish entered into waterways they reproduced prolifically and have reached populations that suffocate the rest of the ecosystem. This isn't something that happens over the course of a decade either; asian carp species can overrun an ecosystem in as little as 2 years which means you can lose your favorite fishing spot in no time. This highlights need for anglers to be proactive in the fight against invasive species and do their part in stopping the spread.

Todays invasive species is Grass Carp!

Grass Carp is one of four species of invasive Asian carps. The spread of Grass Carp, in particular, has largely been the result of intentional stocking in lakes to control aquatic plants. There are currently no established populations of Asian carps in the Canadian waters of the Great Lakes. However, researchers have found evidence of Grass Carp reproduction in two U.S. tributaries of Lake Erie – making Grass Carp the most immediate threat of the four species of Asian carps to the Canadian waters of the Great Lakes.

Grass Carp can eat up to 40% of their body weight a day in aquatic plants and reach up to 5 ft long and more than 80 lbs in weight – that’s a lot of aquatic plants! To put this into perspective 32 lbs of plants a day is roughly a bathtub packed full! Most weedbeds are sparse and so this is a ton of weeded area to lose every single day. Think about how small your favorite weedbeds are to fish and that a single grass carp could it in its entirety in a single day. Just 10 Grass Carp per hectare can reduce aquatic vegetation by up to 50%. This is a huge threat to the Great Lakes ecologically and economically. Grass Carp would cause serious negative impacts to many native bird and fish species that depend on aquatic plants for habitat, food and nursery sites. Grass Carp only digest about half of the plant material they eat and expel the rest back into the water, decreasing water quality. They quickly outgrow the gape (mouth) size of any potential native predators and are extremely difficult to control where they establish.

Grass Carp have large scales and a short, narrow and rounded dorsal fin with no spine. Their eyes sit in the middle of their head and they don’t have barbels. Their dorsal fin starts slightly ahead of the pelvic fin and their anal fin is short in length and doesn’t have a spine. Learn more about Grass Carp identification and check out some commonly confused species at the link here.

You may be wondering why anglers and specifically you should care about this species. If you are an avid outdoorsman or fellow angler here are some of the impacts that grass carp can have on your favorite waterbodies and species. At a high level they will quickly become the only species left in the body of water:

Walleye: Walleye are known to deposit eggs within vegetation during spawning season. Grass Carp eat up to 40% of their bodyweight a day in aquatic vegetation, which would decrease the spawning success for Walleye.

Smallmouth Bass: Due to the voracious diets of Grass Carp, they have the ability to outcompete many native species and organisms for resources. This could dramatically alter the food web that Smallmouth Bass rely on as a top predator.

Muskellunge: Much like Northern Pike, Muskey use aquatic vegetation to help ambush predators, and even deposit their eggs when spawning onto this vegetation. Due to the voracious diets of grass Carp, who consume up to 40% of their body weight a day in aquatic vegetation, this species would experience negative impacts that reduce their spawning success and ability to ambush predators.

Yellow Perch: Yellow Perch typically use aquatic vegetation for spawning grounds and to help hide from predators. Since Grass Carp can eat up to 40% of their body weight a day in aquatic vegetation, they would significantly reduce suitable habitat locations.

Northern Pike: Northern Pike are opportunistic feeders that use areas with heavy vegetation for feeding and lurking. They are also known to spawn randomly within patches of vegetation and deposit their eggs onto aquatic plants. Due to the feeding habits of Grass Carp, Northern Pike would experience negative impacts on spawning and predatory success.

Largemouth Bass: Largemouth Bass are usually found in dense vegetation. Grass Carp can eat up to 40% of their body weight a day in aquatic vegetation, putting Largemouth Bass at risk for habitat loss.

There are a number of ways anglers can help stop the spread of Grass Carp. First & foremost comes with being aware of the risks this species has to our water bodies and reporting any sighting. We can train ourselves to learn how to identify and report Grass Carp. Download the identification and reporting guide here. Should you find yourself in a situation where you have spotted or caught a grass carp take a photo, note your location and report it to the Invading Species Hotline: 1-800-563-7711, or, or and follow the remaining steps. If you are not able to reach someone directly, do not release the fish alive. Kill, gut and keep the fish in a cooler, with its head above the ice. Report it – Fisheries and Oceans Canada (DFO) will collect it.

For more information regarding Grass Carp & identification check out the fact sheet here!

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