“Carp-e diem”—Sampling for Invasive Carp on the Chicago River

It’s 6:30 in the morning, and the boat is already quietly cruising up the river. We’re in the middle of a canyon, its dark walls beginning to glisten in the cool light of dawn. The canyon boasts sheer walls hundreds of feet high, but they aren’t made of rocks and soil. Instead, this canyon is made of steel, glass and concrete, crossed by spans of bridges carrying cars and pedestrians on their morning commute. They might be on the hunt for their morning coffee fix, but, down below on the river, we are hunting something else entirely. In the middle of downtown Chicago, we are seeking the invasive bighead and silver carp.

Looking like slimy, silvery torpedoes with big toothless heads and low-set eyes, invasive carp would not win any beauty pageants in the fisheries world. But it’s not their looks that are the problem—it’s their behaviors that make them a threat to our native systems. Bighead and silver carp are filter feeders, feeding on the tiniest of plankton that forms the base of the aquatic food web upon which all riverine life ultimately depends. They grow quickly, frequently reaching weights of more than 20 pounds, and in some cases, in excess of 100 pounds. Large fish consume large amounts of plankton. They also can produce large amounts of eggs. Silver carp also have the behavioral quirk of throwing themselves out of the water with wild abandon at the slightest disturbance like a team of crazed synchronized swimmers. Though often comical, these explosive reactions can be dangerous to unwary boaters.

On this particular morning, however, the large schools with hundreds of invasive carp are far downstream. If we turned around on our journey and followed the river south out of Chicago, we would need to travel for almost 50 miles, transit though two navigation locks, and pass through the highly electrified barrier defense system before we reached the carp invasion front near Channahon in Will County. If we wanted to reliably encounter large numbers of carp, we’d have to go even further. But our work today isn’t about filling an entire boat with carp. Instead, it is all about looking for that one sneaky fish. The Chicago Area Waterway System holds the dubious honor of being the largest continuous location where invasive carp could pass from the Mississippi River watershed into the Great Lakes, so it is critical that the river is monitored for the presence of any carp that may have circumvented downstream defenses. Our boat crew today will be sampling right at the Chicago Lock, the final barrier separating the Chicago River from the grand expanse of Lake Michigan.

Unlike the many commuters in business attire in the streets up above, we are dressed in bright orange PVC waterproof bibs and jackets, looking appropriately like pumpkins for this chilly October sampling effort. This early in the morning, the river is still quiet, but soon it will be bustling with boats. Our goal is to conduct much of our sampling early, before the river becomes too crowded.

Our boat captain checks his side-scan sonar, looking for any suspicious large fish to target. We are setting long panels of gill net in the river, with mesh perfectly sized to ensnare an invasive carp. By the time we lay out all 200 yards of net, the mesh stretches along the river’s edge for more than a city block. In downtown Chicago, the riverbank is simply a vertical bulkhead, with the Chicago Riverwalk at the edge.

We are now operating alongside the daily commuters and dog walkers, and we receive several confused looks as we begin to rev the boat motor, spraying water in a rooster tail out behind the boat. The goal of this activity is to startle any nearby fish right into our net, which is then expertly hauled back into the boat. Entrapped in this net are three common carp, large and yellow with long barbels by their mouth. This is not one of our target species, so we remove the carp from the nets and release them back into the river, with only a slippery layer of slime left on our clothes as a memory. A few onlookers look boggled at the size of these fish, and at least one phone is whipped out for a quick TikTok video.

After a dozen repetitions of setting and pulling net, we have not encountered any bighead or silver carp and have covered almost the entire shoreline of the main stem of the Chicago River. The hardest set of the day is a mysterious piece of debris on the river bottom which almost takes part of our net with it. Even so, with the early start to the day, we decide that we have enough time to move locations.

After taking the boat out, we drive 20 miles south to the Calumet River, which connects the Chicago Area Waterway System to Lake Michigan at the busy Port of Calumet. The character of this river is very different from this morning. Rather than elegant high-rises, the shores are filled with industrial sites. Scrap metal piles and mounds of brightly colored powder are interspersed with silos, which load raw materials onto barges with huge pipes. We are meticulous with our sampling here, as two silver carp were caught a few miles away in Lake Calumet in 2010 and 2022. One was caught by this very boat crew. The sun is out, but the wind has picked up, and we struggle to stay on course, especially with a seemingly endless parade of sailboats coming from Lake Michigan.

On our way, we pass two other carp sampling crews. These teams are using electrofishing rather than gillnetting to target carp, which provides a useful complement to our netting efforts. Several agencies are participating in this sampling effort led by the Illinois Department of Natural Resources (IDNR), including the Illinois Natural History Survey, U.S. Fish and Wildlife Service, and U.S. Army Corps of Engineers, and additional IDNR-contracted netting teams.

In over two weeks of sampling, crews this fall conducted 72.5 hours of electrofishing across 312 different locations and set 50.5 miles of gill net at 444 different locations. No bighead, silver or grass carp were found. This sampling is conducted in Chicago each year in the spring and fall and provides the best assurance that there are no carp present upstream of the invasion front 47 miles from Lake Michigan. Outside of these sampling events, intensive carp harvest takes place downstream, removing millions of pounds of invasive carp from the lower Des Plaines and Illinois rivers each year.

As our day finally comes to a close, there is one final stop to make. A quick stop under the 95th Street Bridge (made famous in the Blues Brothers movie) and a madcap scramble up the steep, overgrown riverbank takes us to Calumet Fisheries, a popular local seafood shack. Now fully stocked with some delicious fried and smoked snacks, we hop in the boat for the ride home, satisfied with our work for the day and ready for more work in the future to keep the Great Lakes free of invasive carp.