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.
