Three Asian carp caught in the Humboldt Park Lagoon have joined the display of invasive species at Chicago’s Shedd Aquarium.

The carp are huge, old and beady-eyed to boot. So how did they show up in an enclosed lagoon in the middle of Chicago?

“Nobody can say for sure,” said John Rogner of the Illinois Department of Natural Resources. Fishermen and boats could have accidentally brought carp into the lagoon by introducing even small amounts of organic matter from another waterway.

And these fish are more than 10 years old, which means they’ve likely been hanging out in Humboldt for a while.

Rogner said the DNR itself could be the inadvertent source. Chicago-area lagoons are stocked each year with loads of fish including bluegills and catfish for urban fishing programs run by the DNR and the Chicago Park District. The DNR only started closely monitoring those loads for Asian carp minnows a few years ago, when it became evident the giant fish were creeping closer and closer to Lake Michigan.

The carp are now a dominant presence in some parts of the Illinois River, which is connected to the Chicago River via the Sanitary and Ship Canal. 

The DNR hires commercial fishermen to catch Asian carp in the Illinois River. The DNR says they remove hundreds of tons of carp a week, most of which are ground up for organic fertilizer.

But even with two electric barriers in place and a third under construction to block passage into Chicago’s waterways, Asian carp get around. The Humboldt Lagoon carp are a great example; the lagoon isn’t connected to another waterway, yet there they are.

Rogner said fishermen and boaters should never dump water or fish from one waterway into another because there’s a danger of inadvertent transfer. It’s now illegal to possess or move a live Asian carp.

“We just cannot take that risk,” said Rogner. “And people, especially fishermen and others who might be in a position to move these fish around, need to be aware of that.”

The DNR gave the carp to the Shedd to raise awareness about the risks posed by invasive species. If Asian carp make it into the Great Lakes, scientists and environmentalists say it would devastate the ecosystem.