Science Friday - Can A Billion-Dollar Barricade Keep Carp Out Of The Great Lakes?

Episode Date: November 5, 2025

Decades ago, non-native carp were brought onto fish farms on the Mississippi River to control algae and parasites. They escaped, thrived, and eventually flooded the Illinois River, outcompeting native species and wreaking havoc. If the carp find their way into the Great Lakes, they could do major damage to those vital ecosystems.There’s a proposed project to stop the fish—but it’s expensive, and not everyone agrees it’s the best solution. Host Flora Lichtman speaks with WBEZ and Grist reporter Juanpablo Ramirez-Franco and carp expert Cory Suski.Guests: Juanpablo Ramirez-Franco is an environmental reporter at WBEZ and Grist. Dr. Cory Suski is a professor of aquatic resources at the University of Illinois.Transcripts for each episode are available within 1-3 days at sciencefriday.com.  Subscribe to this podcast. Plus, to stay updated on all things science, sign up for Science Friday's newsletters.

Hey, it's Flora Lickman, and you're listening to Science Friday. Today in the show, drama with invasive carp and how to keep them in check. It's absolutely raiding fish. And part of it is that they actually have to be like strapped into the boat to make sure that nothing goes wrong. Because these are big fish. They can be like over two feet long, way like upwards of 25 pounds. Now it's time to check in on the state of science. This is KERNO.

St. Louis Public Radio News. Iowa Public Radio News. Local science story. of national significance. Today we're turning to the Illinois River for a fish tale gone wrong. Decades ago, non-native carp were brought onto fish farms on the Mississippi River to control algae and parasites. They escaped, thrived, and eventually flooded the Illinois River out-competing native species and generally wreaking havoc. Environmental managers have tried to control the fish without much success, and now one of the

biggest fears is that these carp will find their way into the Great Lakes. via Chicago and do damage. There's a proposed project to stop the fish, but it's expensive and not everyone agrees. It's the best solution. Here to tell us more is Juan Pablo Ramirez Franco, environmental reporter at WBEZ and Grist. He's based in Chicago. Juan Pablo, welcome back to the show. Hey there, Flora.

Happy to be here. Okay, so you went on a boat with these researchers studying the carp. Set the scene for me. What was it like? Sure. So we were lucky. You know, it was this sort of breezy, easy, late summer. day and we were on board something called an electrofishing boat. Effectively, it's this like

20 foot long aluminum boat and the funny part about it is that it has these like two long sort of arms at the bow of the ship that when the captain of the ship is like ready, he like drops them into the water and then he hits the button and this generator pumps electricity into it and sends an electric shock into the water which will stun most fish. That's the idea except for the invasive carp. Now, when they get shocked, they like fly out of the water, and I'm not talking like a foot, two feet. They'll fly like 10 feet to 12 feet out of the water. And at the bow of the ship, there are these two fish technicians who are there with like nets, ready to catch them and wrangle them back in and put them in these live wells so that they can be in.

Wait, wait. So it's raining fish and you have people at the front of the boat with nets who are just sort of trying to catch them in midair? It's absolutely raining fish. And part of it is. is that they actually have to be, like, strapped into the boat to make sure that nothing goes wrong. Because these are big fish. They can be, like, over two feet long, weigh like upwards of 25 pounds. And so they have to be strapped in to make sure that they don't accidentally fall out while they're doing this. Wow, that is a wild image. And what are they trying to catch?

Is it one species? Is it multiple species of carp? Totally. So what they're actually doing is they want to get a sense of all of the species in a given area. So they're not just looking for the invasive carp exactly. They're also checking to see on native fish. How are they doing? Because part of what's going on with these carp is that they're eating the very bottom of the food chain.

So they're not leaving a lot of food for these other guys. So when they look at these native fish, if they see that they're skinnier or not so big, they know something about the kind of impacts the carp is having just on that ecosystem. And what are they trying to learn from these surveys? Yeah. So the big idea here is that scientists in Illinois want to know where the carp are and where they're doing well. And so by knowing the abundance of carp in certain parts of the river, they can know where they should be focusing harvesting efforts. So that's like the state's only tool to really get these fish out, which is hiring commercial harvesters, that's commercial fishermen, to get these fish out.

The state will pay fishermen something like 20 cent extra per pound of carp. They also do these just like giant commercial harvests. These are like these targeted harvesting events like over a couple days. So at one point, a couple years ago, they took out something like 750,000 carp just like in a single harvest, which is unreal, right? But the state has also been taking other steps. So like, for example, a couple years back, the state tried to rebrand or they did rebrand the carp to something called Copey, to try to get people to want to eat this fish. so that there was a sort of market solution to an invasive problem. And they thought if they just gave it a new name, that people would be like, sure.

Well, you know, in their defense, there's a lot of cases where this has worked where people change the name of like, I think it's like Patagonian toothfish to like something else. Let's talk about this giant fish blocking infrastructure project that's been proposed. What is it exactly? Yeah. So, Flora, you're talking about the Brandon Road Interbasin project. This is a decades-long plan to sort of wedge in this underwater defense system into the river to make sure that the carp stay contained and don't get any closer to the Great Lakes. And so basically it's like this upgrade to a lock and dam already existing.

But with some more bells and whistles to make sure the carp don't even get any funny ideas. Such as? Such as a bubble curtain. So this is some continuous jets of bubbles that just like are meant to. deter the fish, these underwater speakers that make this noise that the fish are supposed to not like. There is an electrical barrier to really shock the fish just in case. And also a mechanism inside the lock that flushes them and make sure that they really cannot get through. So is it approved? Where is it on the road to reality? So we are very much at the very beginning

of all of this. So it got some approval back in 2020, but even then it's hit some roadblocks in the way, especially around who's going to finance it, the state of Illinois and other Great Lakes States have been working with the federal government to figure out, is there a way to shift some of these costs onto the federal government and away from Illinois in particular? How much would it cost? In total, it's something like $1.15 billion. So not a small ticket item. Wow. And is it controversial in any way or do people mainly agree? Like, yes, this is what we should do. Yeah.

So I would say that when you talk to scientists and local officials, something that you'll hear a lot is that no one wants to find out what happens if they ever make it past Chicago. When you talk to opponents of it, what they'll say is that there are cheaper ways to do this. They'll say that maybe you could just close the lock and dam and just no more barge system. And then all of a sudden, you don't have to worry about the transfer of the invasive carb. Juan Pablo Ramirez Franco is an environmental reporter at WBZ and Gris. and he's based in Chicago. Thanks for coming on today. Thanks so much.

We have to take a break, but do not go away because when we come back, we're diving into the biology of these fish. Our invasive carp, the cockroaches of the water. They grow quickly. They're very abundant. They can have lots of offspring, and nothing can eat them.

So they just become numerous. They just sort of like spread. They're just insidious. As we consider the pros and cons of this fish fortress, You might wonder if these invasive carp are so hardy and so successful in these Midwest waterways, why haven't they made it to the Great Lakes already? To find out, we called up a scientist who has studied this very question. Dr. Corey Susky is a professor of aquatic resources at University of Illinois.

Corey, welcome to Science Friday. Hi, thank you for having me. Okay, these fish have been in the Illinois River for decades. Is it surprising they haven't already made it to the Great Lakes? Yeah, somewhat because they've been doing a really good job of spreading themselves around at a bunch of other locations. But for some reason, in the Illinois River, they've stopped moving farther north, closer to Chicago and closer to the Great Lakes. So why? There's a lot of possible answers for that.

For example, there's a really active suppression effort that's been going on downstream, trying to drive the population down. And as you get closer to Chicago, the habitat changes, meaning it changes from like a natural river to an engineered channel and the banks get really hard and get really armored and they're sort of like walls. And so it gets to be a very different river as you get closer to the city. So that could be deterring the fish. And the area that we've been looking at is maybe there's something in the water that they don't like that is keeping them from moving farther north and closer to the Great Lakes. There's something in the water around Chicago. Is that the idea? Yeah, something coming from the city because the water is flowing from north to south, right?

It's leaving the city down the Chicago-Rey waterway system. And so what we've been asking and wondering is, is there something there that's in the water that they don't like it? Because animals will do that. If there's something in their environment that they don't like, they will just swim away. They will just leave. So, yeah, it's not really for me. I'm just going to go elsewhere. Well, what have you found?

There's a bunch of different pieces that have all kind of come together. So first of all, there's been a bunch of work looking at water quality and doing water quality monitoring in that part of the river. and there's a lot of different chemicals and different compounds in the water that come through the Chicago Area waterway system. Some of them you'd expect and some of them, like, you know, there's just sort of runoff from parking lots. So we know that as you get closer to the city, the water is very different than it is if you were to go farther downstream. And interestingly, the composition of the water changes right around the leading edge of carp. So there's sort of that correlational relationship between water quality and carp distribution that seems to fit

together, but that's sort of correlational. Right. Okay. And you did a study on this, right? How did you actually do this work? So we did a couple different things. So basically, we're interested in, is there something there that the carp don't like that caused them to not swim closer to Chicago? So to test that, we were not able to move carp closer to Chicago. That's actually a good thing. Because you don't want them to escape. Right. Exactly. We're not going to like, you know, run that risk. But what we're able to do. Create the problem that you're trying to avoid. Exactly. And then say, look, I told you. So what we were able to do, though, is move water.

So we went to the Chicago Area Waterway System and we grabbed water from a little bit farther upstream than carp are currently located. And we moved it to fish hatchery at the across Wisconsin at the USGS fish hatchery there where they grow baby carp. And we're able to place baby carp from the hatchery into water that would essentially represent a range expansion. mansion and would be from an area where they are not currently found. You're simulating basically the carp going to this part of Chicago's waterways that they don't typically go. Correct. Where we've basically never really seen a carp before.

What if we just put them in that water and try and see what happens? What happens? So two things happen when you put them in the water. First of all, their metabolic rates go up. So they start burning more energy. And we're thinking that this is because they're processing some pollutant and processing some toxin that they weren't exposed to downstream. And so, again, it's a higher energetic load and a higher energetic cost when they're

in that water closer to Chicago. And then the other thing that we saw was that they actually stop moving. And they more or less freeze when you just put them in the water. So that's a response from animals when something is wrong in their environment, they sort of have two choices. You can freeze or you can flee. And so you flee, you just get out of there because you're like, oh, this is terrible I'm leaving.

Or you freeze and you sort of like hunker down. you kind of ride it out and you hope it kind of goes away. And so what we saw then with the carp is if you take them and move them into water closer to the Great Lakes where we normally don't find them, they burn more energy, but they move less and they actually stop moving. Yeah, that's perplexing. I mean, did you get any clues on which pollutant is the carp tonight? No, because there's a lot of things. I guess I said, there's a lot of things in the water and it could be, you know, it could be to do with concentration or it could be to do with just what's there, what's not there. it's kind of a, yeah, there's a lot.

There's a lot to kind of pick through. Another study that we did then was we took a similar kind of thing. We sort of moved the water down to Havana, Illinois, toward the population core. We looked at stress levels and the genes in their olfactory nerves. And what we see is that if you take those fish and put them in water, that would be closer to Chicago, they have increased molecular indices of stress in their olfactory nerves. Hmm. So there's something in their.

olfactory system. The analogy would be like there's just something there kind of a tingling and something unpleasant from an olfactory perspective that they don't sort of like. Do native fish have this problem? I mean, are other fish blocked by this whatever's in the water around Chicago? Interestingly, no, because for a number of different reasons, when the study where we took fish to the fish hatchery in Wisconsin, we ran a similar series of tests with some native fish with the minnow, super popular all across the Midwest and super popular in the Chicago area waterway. And they really didn't show the same response. Are they just tougher city fishes?

I don't know if it's toughness or if there's just something maybe less sensitive or less sensitive olfactory systems or something. We're not really sure. The other thing is that we do know that the water quality in the Chicago area has been improving over the past few decades. Fish communities are growing. They're getting more healthy, it's becoming more diverse. So there's a lot of good things happening.

And so the point is whatever's going on in the city water, the native fish community seem to be fine with it. And they seem to be trending in a really good direction. I mean, if the carp don't like the water in Chicago, is that a reason not to build this barrier? No, I don't think, I think we want to keep building the barrier. Like, I think it's a little bit tenuous. You know, because, again, there's a lot of good work that water quality is improving.

And I think that what we're trying to highlight with some of this work is that if something changes with the water, we could see carp start to move all of a sudden. Like where it's kind of almost like where it's really fortunate, they haven't moved, and they've been kind of stable, and that's kind of working in our favor and that's bought us some time. But we don't really know what's going on, and that could change. And then suddenly we're going to find that carp are now farther north. They're a little bit closer to the Great Lakes, and we don't want to be caught off guard by that. This is so dystopian, but are people like, well, this is a good reason not to clean up the water around Chicago.

Yeah, this is not a call to continue polluting or to prelude. promote pollution. But having said that, if we can figure out the compound of what it is, maybe there's a way to sort of like take advantage of it or like, you know, recreate it or something. Like again, until we sort of figure out what the silver bullet is there, it's a little bit tough to make predictions about what we could do. What makes them so hardy? I mean, generally speaking. Should I be thinking of them as like the cockroaches of the river, like indestructible omnivores that have a lot of babies or like, what's their secret sauce? Yeah. So I don't know if it's that they're indestructural.

I think a lot of it just has to do with numbers. Like where and why and how they spawn and have reproductive events is still, I mean, we have sort of broad general cues. They like that they spawn in the spring and they spawn when the river levels go up or whatever. But it's tough to make predictions. Like, you know, they don't spawn every spring. They don't spawn every time the river levels go up. But when they do go up, there's,

there can be huge spawning events and they can have lots and lots of offspring. So they can repopulate things really, really quickly. They grow pretty fast. and then they do reach a large size that makes them invulnerable to other predators. So a one-year-old carp is very big compared to a one-year-old like a bass or a bluegill or something like that. And so they just escape, nothing can eat them. So they grow quickly. They're very abundant.

They can have lots of offspring. So they just become numerous. They just sort of like spread. They're just insidious as opposed to just being like cockroaches that are just really, really tough. Where do you take your research next? So we would like to try and find out what it is in the water, at least get it close. There's a cool example from the West Coast of coho salmon that we're dying, and a group is asking similar questions.

And you can sort of fractionate the water. You can say, well, let's take out the organic compounds, or let's take out this type of compound. You can sort of strip down the water and repeat those tests with water of different fractions. And you might not be identified the specific chemical, but you can at least get like a class of chemicals or like maybe it's a compound that's coming from petroleum products, or maybe it's a compound that's doing this, or you can sort of identify that. And a group that's on the West Coast, they had co-host salmon that were dying in rivers, and they managed to fractionate the water and separate it all out, and they traced it back to a compound that comes from car tires. So you

can find that needle in the haystack. Good luck. Thank you. Dr. Corey Susky is a professor of aquatic resources at the University of Illinois. Corey, thanks for taking us through this whole kettle of fish today. Thanks for inviting me. Okay, before we climb off this fish ladder, a few weeks ago, we did a story about lab-grown salmon. In that story, we blithely dropped an idiom. We said the amount of lab-grown salmon produced is a drop in the bucket compared to how

much salmon is consumed. Now, listen, we know y'all are nerds. Why else would you be here with us? but we may have to bestow the close listener crown on James from Issaacca Washington, who did some actual math on whether lab salmon really is a drop in the bucket or not. Here's James. At best, less than 10 tons of meat is produced in the lab. So we'll just say 10 tons.

Approximately 3.8 million tons of salmon are harvested each year. That is a ratio of 380,000 to 1. There are 591.5 drops in an ounce, multiplied by 128 ounces per gallon, and five gallons in many standard buckets. This comes to 378,541 drops in a bucket. So lab production is pretty exactly a drop in the bucket. Thank you, James. We loved your message. And if you want to leave us a voicemail to fact-check our metaphors or about anything else, the number is 877 for SciFri.

We love hearing from you. Today's episode was produced by Kathleen Davis. I'm Flora Lichtman. Thanks for listening.