In the mid-20th century, across the United States, wastewater plants and other ponds started to import a few species of fish, mainly bighead carp and silver carp. Those are fish that are particularly good at consuming algae blooms and other pests. And as with many things from the mid-20th century, what was meant to be a quick and easy solution turned into an ecological nightmare, because, of course, the carp escaped into the wild during floods. Of course, they out-consumed and out-competed all the local species. And of course, they have no natural predators. So in parts of the Mississippi and Illinois rivers, like here in Peoria, those carp make up 95% of the entire fish biomass. The ecosystem that was here has basically been destroyed and replaced by carp. They can weigh more than 30 kilos and they are easily startled. They will jump out of the water at the slightest disturbance. If you go past a school of them in a boat like this, well, you can see what's happening. If one of those hit you in the head, it could do serious damage. Loads of YouTube channels have already talked about these carp-filled rivers because it's a big visual story and a great demonstration of human intervention causes harm. But the big problem right now is where these fish could end up next. And hopefully, by the time I get there, the weather will have got a bit better. The Great Lakes of North America have a $7 billion fishing industry and a $16 billion recreational boating industry. If those carp reached the lakes, it would be another ecological disaster. And the lakes are connected to the Illinois River and the carp in one place, the canals of Chicago. This here is the choke point, the Chicago Sanitary and Ship Canal. The fish would have to come through here, which is why this water is electrified. The US Army Corps of Engineers have put a giant electric fence underwater. We have chosen this point very strategically so that there's no way for invasive carp to get around this one particular point and get past the barrier into the Great Lakes. This is also a man-made canal, so it's a very standard shape, and we have the electric bars that bring the electricity into the water sitting nearly on the bottom, 21 feet below the surface. The barriers are designed to send DC electric current into the water. It's pulsed into the water very fast to create a voltage gradient in the water, like a speed hump that you would see on a road. For barrier 2A and 2B, it's 2.3 volts per inch at the surface, and at barrier one, we're aiming for something around 6.0 volts per inch, and it creates this barrier of electricity. The actual rooms with the pulsers, the things that send the electricity into the water, are off limits behind blast-proof doors. I can show you photos, but I can't go in because banks of capacitors that can store and release enough energy to electrify all this water 34 times a second are extremely dangerous. On certain days, you can actually see fish swimming upstream and then they'll turn around and come back. If a fish is brave enough or gets pushed far enough into that voltage gradient, it will stun them, and then they would just float back downstream and they'll wake up somewhere and not understand why they got there. We have fish biologists for making sure that the barrier works. They go out, they capture fish, they tag them, and then they release them below the barrier. The fish do not get past the barrier. We do know that the 2.3 volts per inch is not as effective against little fish. The main population of the invasive carp has reached about 70 kilometers away from here, and over the last few years, it hasn't seemed to move any closer, which is a good sign, but it doesn't stop individual fish from making the journey. They've been found much closer, even occasionally on the wrong side of the barrier, and all it would take is a few to make it through, and suddenly, the Great Lakes have carp. When the barrier had to be shut down for maintenance in 2009, toxin was added to 10 kilometers of this canal to kill everything in it, just in case. The amount of voltage that we have to send into the water to keep the barrier operating goes up dramatically when a barge comes through. We've noticed with some of the smallest fish actually do tend to go through the barrier when a barge is going by because of that voltage sag. So we do know that's that is one weakness of the barrier. Barges are built with what's called a rake on the front. That's the angled portion of the barge. They put it sometimes in between two barges, and so there's a water space in there and they found that under certain circumstances, small fish could stay in that portion of water for for many miles traveling up a river. And so there's the concern that a barge could take a small fish and make it through the barrier. The Navy dive team came out here and did a study on the electricity in the water and what that might do to a person. And the conclusion of that study was that there was a greater than 50% chance that someone in the water would experience cardiac arrest and would die. The Coast Guard has established special rules for this area. There can be no personal watercraft, so no jet skis, no canoes, no kayaks that can go through. All barges passing through this area are required to use steel cables as well so that the potential between barges stays the same. Many times barges like to have people out on the bow or out on deck doing things. They're required all to be inside in the boat while they're traversing the barrier. Yeah, the birds are totally fine. It's like birds standing on an electrical wire. They gather around and they see these fish kind of gathering at our barrier area and they swoop in and get them. One of the reasons that we have multiple barriers is that they do require maintenance. And so when we have a requirement to maintain a piece of equipment, we make sure that one barrier is operating. We have this layered defense, basically. The connection between the Great Lakes and the now carp-filled river isn't natural. It was made by engineers 100 years ago in one of the largest civil engineering projects America's ever seen. The entire flow of the smaller Chicago River was reversed in order to flush sewage and waste water out of the area. So in theory, that connection could be closed again, back to how it was in the 19th century. But that would involve re-engineering most of Chicago's big waste water systems and flood defenses, and it would cut off what's now a major route for shipping and boating. Closing the link has been suggested, there have been lawsuits about it, but it's not happened. There's millions of dollars worth of goods that traverse just through this area alone. Barge traffic would have to find another way to get to its end goal. That would often result in more trucks, leading to congestion, leading to more pollution. So, although the easiest solution is to close the canal or close a lock, it closes off this vital waterway that keeps goods moving in the Great Lakes. We know there are weaknesses, we still work hard at improving the efficacy of the barriers to continue to look at what voltages are needed to deter fish. Do we have the right millisecond settings? Do we have the right voltage settings? We're even looking at adding things like lights and sound or possibly even CO2 to the barrier defenses. And so we're continuing to bring that research to bear and provide the best deterrent that we can to keep the invasive carp out of the Great Lakes. So, for now, the electric barrier pulses away. And back out in the Illinois River where I started, a whole new industry has been set up catching carp.
A man stands on a moving boat under a canvas canopy, speaking directly to the camera.
"In the mid-20th century, across the United States, wastewater plants and other ponds started to import a few species of fish, mainly bighead carp and silver carp."
Setting: on a boat on a wide river — overcast, diffuse daylight
People (1):
• standing, turned slightly towards the camera, wearing maroon t-shirt, short, light brown/graying hair — speaking, expressive, wide-eyed
A large, silver fish leaps high out of the water in an arc, then splashes back down.
"Those are fish that are particularly good at consuming algae blooms and other pests."
Setting: Illinois River — diffuse daylight
Multiple silver fish jump out of the churning wake behind a moving boat.
"because, of course, the carp escaped into the wild during floods. Of course, they out-consumed and out-competed all the local species."
Setting: Illinois River — overcast, diffuse
The man on the boat continues speaking to the camera, gesturing with his right hand.
"So in parts of the Mississippi and Illinois rivers, like here in Peoria, those carp make up 95% of the entire fish biomass."
Setting: on a boat on the Illinois River — overcast, diffuse daylight
People (1):
• standing, facing camera, wearing maroon t-shirt, short, light brown/graying hair — speaking with a serious expression
The man on the boat turns his head slightly and gestures towards the water behind him while speaking.
"They can weigh more than 30 kilos and they are easily startled. They will jump out of the water at the slightest disturbance."
Setting: on a boat on the Illinois River — overcast, diffuse daylight
People (1):
• standing, wearing maroon t-shirt, short, light brown/graying hair — speaking, looking towards the camera and then back at the water
A chaotic scene of dozens of large silver carp jumping out of the churning wake of the boat.
"Loads of YouTube channels have already talked about these carp-filled rivers because it's a big visual story and a great demonstration of human intervention causes harm."
Setting: Illinois River — overcast, diffuse
A satellite view from Google Earth is centered on a town next to a river, then rapidly zooms out.
"And hopefully, by the time I get there, the weather will have got a bit better."
Setting: Lacon, IL (on map) — n/a (map)
Text: "Lacon, IL", "Google Earth"
The man, now wearing a high-visibility vest, stands on a walkway next to a canal and speaks to the camera.
"recreational boating industry. If those carp reached the lakes, it would be another ecological disaster."
Setting: Chicago Sanitary and Ship Canal — bright, sunny daylight
People (1):
• standing, wearing neon yellow and orange high-visibility vest over a maroon t-shirt, short, light brown/graying hair — speaking with a serious and concerned expression
A brown sign with white text points towards a small ditch next to a road.
"The US Army Corps of Engineers have put a giant electric fence underwater."
Setting: Roadside near the Fish Dispersal Barrier Facilities — bright daylight
Text: "← Fish Dispersal Barrier Facilities", "US Army Corps of Engineers logo"
A man in a high-visibility vest and plaid shirt speaks, gesturing with his hands.
"We have chosen this point very strategically so that there's no way for invasive carp to get around this one particular point and get past the barrier into the Great Lakes."
Setting: Chicago Sanitary and Ship Canal — bright, sunny daylight
People (1):
• standing, wearing neon yellow and orange safety vest over a light blue and white plaid button-down shirt, short, dark brown hair — speaking calmly and clearly
Two large red cranes on opposite sides of a canal lower a long, wide metal grid structure into the water.
"sitting nearly on the bottom, 21 feet below the surface."
Setting: Barrier IIB construction site — bright daylight
Text: "Barrier IIB construction, 2011 Photo: Jessica Vandrick / US Army"
A close-up of a stainless-steel framed monitor displaying a complex system diagram with green and red status indicators.
"For barrier 2A and 2B, it's 2.3 volts per inch at the surface,"
Setting: Control room — indoor, fluorescent
Text: "US ARMY ELECTRIC FISH BARRIER"
A black sign with white text is mounted on a white wall next to a gray door.
"The actual rooms with the pulsers, the things that send the electricity into the water, are off limits behind blast-proof doors."
Setting: Inside the barrier facility — indoor, functional lighting
Text: "DO NOT ENTER WHEN RED LIGHT IS FLASHING"
A still photo shows a room filled with large gray electrical components (capacitors) connected by thick black cables.
"I can show you photos, but I can't go in, because banks of capacitors that can store and release enough energy to electrify all this water 34 times a second are extremely dangerous."
Setting: Pulser room (photo) — bright, industrial lighting
A slow-motion shot of a large silver carp leaping out of the choppy water, its body curved in an arc.
"swimming upstream and then they'll turn around and come back."
Setting: River — overcast daylight
A wide shot of the barrier facility buildings next to the canal. A highway overpass is in the background.
"They go out, they capture fish, they tag them, and then they release them below the barrier."
Setting: Chicago Sanitary and Ship Canal — bright, sunny daylight
The man in the safety vest speaks to the camera, using his hands to illustrate a point.
"The main population of the invasive carp has reached about 70 kilometers away from here, and over the last few years, it hasn't seemed to move any closer,"
Setting: Chicago Sanitary and Ship Canal — bright, sunny daylight
People (1):
• standing, wearing neon yellow and orange high-visibility vest over a maroon t-shirt, short, light brown/graying hair — speaking, focused expression
The engineer speaks to the camera, explaining the effect of barges on the system.
"The amount of voltage that we have to send into the water to keep the barrier operating goes up dramatically when a barge comes through."
Setting: Chicago Sanitary and Ship Canal — bright, sunny daylight
People (1):
• standing, wearing neon yellow and orange safety vest over a plaid shirt, short, dark brown hair — speaking clearly
A large, weathered barge moves slowly through the canal.
"So we do know that's that is one weakness of the barrier."
Setting: Chicago Sanitary and Ship Canal — bright daylight
The engineer speaks to the camera, explaining the safety study.
"The Navy dive team came out here and did a study on the electricity in the water and what that might do to a person."
Setting: Chicago Sanitary and Ship Canal — bright, sunny daylight
People (1):
• standing, wearing neon yellow and orange safety vest over a plaid shirt, short, dark brown hair — speaking with a serious expression
A white tugboat named 'DANIEL E' pushes a long train of barges through the canal.
"The Coast Guard has established special rules for this area."
Setting: Chicago Sanitary and Ship Canal — bright, partly cloudy day
Text: "DANIEL E"
A white bird, likely a gull, swoops down towards the surface of the dark canal water.
"Yeah, the birds are totally fine. It's like birds standing on an electrical wire. They gather around and they see these fish kind of gathering at our barrier area and they swoop in and get them."
Setting: Chicago Sanitary and Ship Canal — bright daylight
A shot inside an industrial facility shows a complex array of pipes. Some are insulated, and some have labels.
"we make sure that one barrier is operating. We have this layered defense, basically."
Setting: Inside the barrier facility — indoor, fluorescent
Text: "COOLING WATER SUPPLY"
The engineer speaks to the camera, explaining the economic importance of the canal.
"There's millions of dollars worth of goods that traverse just through this area alone."
Setting: Chicago Sanitary and Ship Canal — bright, sunny daylight
People (1):
• standing, wearing neon yellow and orange safety vest over a plaid shirt, short, dark brown hair — speaking calmly
A freight train with yellow cars moves along tracks that run parallel to a dirt road and a chain-link fence.
"in the Great Lakes. We know there are weaknesses, we still work hard at improving the efficacy of the barriers,"
Setting: Area adjacent to the canal — bright daylight
A large wall-mounted display shows a grid of many different CCTV camera feeds from around the facility.
"and so we're continuing to bring that research to bear and provide the best deterrent that we can to keep the invasive carp out of the Great Lakes."
Setting: Control Room — indoor, fluorescent
A tugboat pushes a long barge through the canal, passing by the facility. Social media handles for Tom Scott appear on a lower third.
Setting: Chicago Sanitary and Ship Canal — bright daylight
Text: "tomscott.com @tomscott /tomscott tomscottgo"