Asian carp are a problem because they outcompete native fish for food, destroy aquatic vegetation, reproduce at staggering rates, and physically injure people. Four species, bighead carp, silver carp, grass carp, and black carp, were imported to the United States for use in aquaculture ponds. Through flooding and accidental releases, they escaped into the Mississippi River system and have been spreading ever since, now threatening the Great Lakes and the roughly $900 million annual recreational fishing economy they support.
Four Species, Four Types of Damage
The term “Asian carp” covers four distinct species, each causing its own set of problems. Bighead carp and silver carp are filter feeders that consume massive quantities of plankton, directly competing with native fish that depend on the same food source. Grass carp eat aquatic plants, stripping lakes and rivers of the vegetation that other fish and waterfowl need to survive. Black carp feed on mussels and snails, threatening freshwater mollusk species that are already among the most endangered animals in North America.
What makes them collectively devastating is that they don’t just occupy a niche. They reshape entire ecosystems to the point where native species can no longer thrive.
They Starve Native Fish
Bighead and silver carp eat plankton, the tiny organisms at the base of the aquatic food chain. They eat so much of it that native filter-feeding fish like gizzard shad and paddlefish are left with significantly less food. A NOAA-supported modeling study of Lake Erie projected that if Asian carp became established, they could eventually account for up to 34 percent of total fish weight in the lake. That kind of dominance would come at the expense of native species: emerald shiners could decline by up to 37 percent, and walleye and rainbow trout populations would also drop.
The ripple effects move through the entire food web. Plankton supports small fish, which support larger predators. When carp consume a disproportionate share of plankton, every level above it feels the squeeze.
Grass Carp Destroy Habitat
Grass carp consume anywhere from 20 to 100 percent of their body weight in vegetation per day, depending on water temperature and fish size. They preferentially eat desirable native plants first, leaving invasive species like Eurasian watermilfoil for last. This means they only control nuisance weeds when they’ve already consumed virtually everything else, a scenario that wipes out the plant communities fish use for spawning and nursery habitat and that waterfowl depend on for food.
The damage goes beyond plant removal. Grass carp don’t fully digest what they eat. What passes through them is still green and loaded with nutrients, which stimulates algae growth. The result is a transformation from clear water with healthy rooted plants to a murky, algae-dominated environment. Researchers at Michigan State University have documented lakes where grass carp were stocked so densely that, after consuming every submerged plant, the fish resorted to sticking their heads above the surface to feed on grasses at the water’s edge.
Silver Carp Injure Boaters
Silver carp are easily startled and leap as high as 10 feet out of the water in response to outboard motors, passing trains, rocks hitting the surface, or even geese taking off. At boat speeds above 20 mph, a fish weighing over 20 pounds becomes a projectile. Jumping fish have seriously injured boaters and damaged equipment. Water skiing on parts of the Missouri River is now considered exceedingly dangerous because most silver carp jump behind the boat, directly in a skier’s path.
Explosive Reproduction
One reason Asian carp are so difficult to control is their reproductive output. A single female silver carp can produce hundreds of thousands of eggs per year. Research from Southern Illinois University found that silver carp egg production averaged around 269,000 eggs per female in one sampling year and jumped to a mean of nearly 1.5 million eggs per female the following year. Bighead carp showed similar variability, with averages ranging from about 118,000 to over 777,000 eggs per female across two years.
Their spawning isn’t limited to a narrow seasonal window either. Reproductive investment showed no clear monthly pattern during the growing season, suggesting that spawning is protracted rather than occurring in a single pulse. This extended breeding season, combined with enormous egg counts, means populations can explode rapidly once established in a new waterway.
How Close They Are to the Great Lakes
The leading edge of the Asian carp population in the Illinois River is estimated to be about ten miles downstream of Brandon Road Lock and Dam near Joliet, Illinois. That lock is one of the last physical chokepoints before the waterway connects to Lake Michigan. In 2010, an adult bighead carp was caught in a fishing net just six miles from the lake. In 2017, a live Asian carp was found above the three electric barriers in the Chicago Sanitary and Ship Canal. Several Asian carp have also been found in Canadian waters in Lake Michigan since 2015.
Aggressive removal efforts along the Illinois River may have reduced local populations by an estimated 68 percent, but even reduced numbers don’t eliminate the risk. It takes only a small number of breeding adults to establish a new population.
What’s at Stake Economically
The Great Lakes support a recreational fishing economy valued at roughly $884 million to $901 million per year for U.S. anglers alone, with some estimates ranging as high as $1.66 billion. Species like walleye, which modeling suggests would decline if Asian carp establish in Lake Erie, are among the most popular targets for recreational anglers. A carp invasion wouldn’t just be an ecological disaster. It would threaten the livelihoods of fishing guides, bait shops, marinas, and tourism-dependent communities across eight states.
Federal and state agencies currently spend $47.4 million annually on 45 collaborative projects aimed at preventing and controlling the spread, a significant investment that reflects how seriously the threat is taken.
Barriers, Bubbles, and a Billion-Dollar Project
The primary line of defense right now is a set of electric barriers in the Chicago Sanitary and Ship Canal near Romeoville, Illinois. Testing with surrogate fish species showed that 97 percent of fish were incapacitated at lower electrical settings, and 100 percent at higher settings. But the barriers aren’t foolproof. Aluminum-hull boats passing through can distort the electric field, allowing fish to swim nearly twice as far into the barrier zone compared to fiberglass-hull boats. Seasonal water temperature also affects performance, with fish incapacitated more quickly in cooler months.
The longer-term plan is the Brandon Road Interbasin Project, a $1.15 billion effort to install layered defenses at Brandon Road Lock and Dam. Construction moved into its active phase in July 2024, when Illinois and Michigan signed a partnership agreement with the Army Corps of Engineers. The project will combine electric deterrents, acoustic deterrents, bubble curtains, and an automated barge-clearing system to create multiple barriers rather than relying on any single technology. The first construction increment has $274 million in federal funding and $114 million in state funding committed.
Turning the Problem Into Food
One creative approach to reducing carp numbers is eating them. In 2022, Illinois officials rebranded Asian carp as “copi” to make the fish more appealing to consumers. The meat is mild, high in protein, and low in mercury compared to many popular fish. The logic is straightforward: if commercial harvest becomes profitable enough, fishing pressure could help keep populations in check while removing biomass from the water. Whether consumer demand will scale enough to make a meaningful ecological difference remains an open question, but it represents one of the few strategies that could pay for itself.