The barrier facility looks just like every other stretch of the industrial riverfront several dozen miles outside of Chicago. Coal, gas, and concrete operations joust for space along the shoreline. Stacks send plumes of smoke and flame into the sky. But on this expanse of the Chicago Sanitary and Ship Canal, an alchemy takes place underwater: electrically charged water creates a “fence” intended to stop fish from passing through to the Great Lakes.
This unusually extreme method of aquatic control is run by the U.S. Army Corps of Engineers near Romeoville, Illinois. The facility requires round-the-clock maintenance to keep two electric barriers sending pulses of direct current across a canal that’s nearly 30 feet deep and 160 feet across. The elaborate setup is an attempt to keep out one of the most relentless invasive species in the United States: Asian carp. If these fish ever reach the Great Lakes, the consequences could be catastrophic.
The name Asian carp actually applies to four species of fish: bighead carp, silver carp, grass carp, and black carp. In the 1960s, all four were introduced into commercial fish ponds in the southern United States to help manage algal overgrowth with their voracious appetites, but floods pushed them into the Mississippi River. There, the ravenous fish thrived, becoming one of the fastest-spreading invasives in American history.
Bighead carp, wrote Andrew Reeves in Overrun: Dispatches from the Asian Carp Crisis, “comprised 97 percent of the Mississippi River’s biomass” in the early 21st century. The fish can grow to be larger than 16 inches, often outcompete native species, and have spread thousands of miles away from their initial range. They’re notorious for careening out of the water when startled, slamming into boats and humans with immense force. In the Great Lakes — which are connected to the Mississippi River via the Chicago Area Waterway System—Asian carp would almost certainly decimate local fish populations, ravage the ecosystem, and destroy the $7 billion commercial fishing industry.
“There’s a very real…