Illinois clears major hurdle in containing an invasive fish

The silver carp is big, unwieldy, and requires Joe Greendyk to use both his hands to measure it before tossing the fish overboard into the Illinois River. The nearly 2-foot-long invasive fish, which now overruns the river, has become the centerpiece of a state-run monitoring program to rein in its exploding numbers.

“They’re pretty slimy and pretty strong,” Greendyk, a seasonal fisheries technician with the Illinois Natural History Survey, or INHS, said with his hands caked in fish slime. “So if you don’t grip them right, they’re pretty hard to control.”

For decades, local, state, and federal officials have worried that the voracious filter feeder, which can outeat and outgrow native fish, could bypass Chicago and breach the Great Lakes. The fear is that the carp, which leap out of the water and startle boaters, could reduce populations of native species that locals like to fish for and wreak havoc on the world’s largest freshwater ecosystem and the multibillion-dollar tourism, boating, and fishing industries that rely on it. 

But the fight to keep the carp under control and out of the Great Lakes may now be getting easier. Last week, the state of Illinois announced it had acquired land needed to move along the Brandon Road Interbasin Project, a $1.15 billion barricade aimed at keeping the aquatic menace from entering the channel that connects the Mississippi River Basin with the Great Lakes. 

The Brandon Road Interbasin Project, or BRIP, is an underwater defense system long hailed as the solution to the carp problem. The project, designed by the U.S. Army Corps of Engineers, is slated to be built in the Des Plaines River, which connects the Illinois River to Chicago’s shipping canal, near suburban Joliet. The lock and dam upgrade will deploy a bubble wall, acoustic blasts, an electric barrier, and a flushing mechanism to keep the carp from passing through. 

The infrastructure project hit a wall earlier this year amid friction between President Trump and Illinois Governor JB Pritzker over federal funding and immigration enforcement. Trump froze more than $100 million in federally appropriated funds promised to Illinois. In response, Pritzker delayed an initial land transfer of a 50-acre stretch of riverbed from Midwest Generation, the former operator of a coal-fired power plant near the site of the proposed project, to the state. Without it, the Army Corps couldn’t begin site preparation for the project. 

But by the spring, the Army Corps told Illinois officials it had secured funds to begin clearing riverbed rocks, and Pritzker and the White House resumed efforts to get the project off the ground. Allen Marshall, a spokesperson for the Army Corps’ Rock Island District, confirmed that phase of the project was completed in July. 

Tensions rose again at the end of the summer over Trump’s threats to send in the national guard into Chicago to address crime and increase immigration enforcement. In late August, Trump told reporters in the Oval Office that Pritzker was not cooperating on efforts to get rid of the carp. “The governor of Illinois is affected maybe more than anybody else,” Trump said. “I think until I get that request from that guy, I’m not going to do anything about it.”

Nonetheless, the megaproject is on the move. Last week, Illinois officials announced they had reached a deal on September 30 for the two small upland parcels totaling 2.75 acres required for the project. The donation may, however, end up costing Illinois taxpayers.

Previous reporting from WBEZ and Grist revealed longstanding concerns from state officials over coal ash contamination, the toxic byproduct of burning coal, at the site. Pritzker cited concerns about the cost of cleaning up the toxic mess in a 2024 letter to the Corps. 

“It would be irresponsible to write a blank check to the Corps of Engineers or any other project manager without having a better understanding of what we’re agreeing to for the long term,” Pritzker’s spokesperson said in a statement at the time.

The Illinois Department of Natural Resources confirmed that state officials are currently developing a plan to investigate the site and are reviewing whether any additional land is needed.

But despite these concerns, regional leaders are pushing funding for the project forward. Earlier this month, Pritzker joined six other Great Lakes state governors in submitting a letter to Congress, calling BRIP a “national priority” and urging lawmakers to provide full federal financing for the project. 

The invasive carp — a family of fish that also includes the bighead carp, black carp, and grass carp —  first turned up in the Mississippi River about 50 years ago. Experts say fish began overwhelming the waterway after escaping Arkansas fish farms, where they were imported to help limit algae and weed growth. In the intervening years, the fish expanded their range throughout the river and its tributaries and began dominating the Illinois River in the 1990s. 

In 2019, the INHS partnered with the Illinois Department of Natural Resources to establish a multiagency program to track the relative abundance of the carp up and down the Illinois River. As part of the program, crews of ecologists catch and track the health of the carp and native fish every year between June and October. 

The data helps the state stay ahead of the carp. If carp populations are surging in one stretch of the river, Illinois officials can adapt the incentivized harvesting efforts, the state’s main form of carp control. The program includes contracting with commercial fishermen for targeted catches and paying an extra 10 cents per pound of carp. The effort appears to be working.

“We’re making an increasingly large dent in the population, according to these data,” said Michael Spear, a quantitative ecologist with the INHS. “That incentive seems to be paying off.” He pointed to the area near Starved Rock State, one of the northernmost stretches of the over 270-mile-long river, where he has noted drastic declines in the carp population over the last five years. The state’s Department of Natural Resources did not provide detailed estimates of the carp’s decline at the time of publication. 

Spear watched from the back of the sampling boat as Greendyk and the rest of the crew wrapped up their work for the day. While the data is promising, he said that nobody wants to find out what happens if the carp make it upstream of Chicago.  

“The carp may not be in some of these other Great Lakes states,” Spear said. “But there’s a lot of attention from those states, because if they get into the Great Lakes, it’s going to become a much more regional problem.”