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 these hits 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 reach 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 manmade 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 ⅠⅠA and ⅠⅠB, it's 2.3 volts per inch at the surface.
And at barrier Ⅰ, 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 70km 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 10km 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 that some of the smallest fish
actually do tend to go through the barrier
when a barge is going through because of that voltage sag.
So we do know 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 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 to that study was 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 jetskis, uh, 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.
The birds are totally fine. It's like birds standing on an electrical wire!
They gather around and they see these fish gathering at the barrier area
and they swoop in and get 'em.
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 a hundred 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 wastewater 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 wastewater systems and flood defences,
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.