Wending through corn and soybean fields southwest of Chicago, the Illinois River eventually comes to the sleepy little town of Havana, Illinois. On the east bank of the river, the populated side, there is a field station run by the Illinois Natural History Survey. For decades now, INHS biologists in aluminum skiffs have scooted up and down the thinly wooded banks, monitoring local fish—these days, catching, recording and releasing approximately 150,000 of them a year. The local species are small and nondescript for the most part; their behavior is unremarkable. Probably the most colorful thing about these fish is their names: gizzard shad, bigmouth buffalo, largemouth bass, bluntnose minnow—hand-hewn names from America’s heartland.
In the mid-‘90s, though, the lazy stretch of river around Havana was roiled by the invasion of two species of Asian carp, the bighead carp and its flamboyant cousin, the silver carp. Imported from China during the 1970s, the carp escaped their ponds in the South, migrated up the Mississippi River, and spread into tributaries like the Illinois. “They puttered along for a few generations,” says Duane C. Chapman, the top Asian carp expert for the U.S. Geological Service, “and then they reached an exponential growth phase.” A quirk of silver carp behavior—an exaggerated startle response, causing them to leap from the water when boats approached—revealed their enormous, unexpected populations in the rivers of the Midwest. Along La Grange Reach, as this section of the Illinois is called, routine monitoring tasks took a dangerous turn. Today, the biologists have to measure the local species amid a glut of flying aliens.
“You’re sitting in the kill zone,” Thad Cook remarked to me, as the skiff pulled away from the launch site. Cook, director of the INHS station, was driving. He sat behind a low shield in the stern, but the visitor’s chair beside him was exposed. I stood up nervously, holding onto a strut. I recalled reading about a woman who nearly died while riding a Jet Ski near Peoria, upstream from Havana, in 2004. She was knocked unconscious by a silver carp and tumbled into the river. “We’re at ground zero,” Cook warned, smiling. “The carp don’t wax and wane here.” In a video I’d watched on the Internet, a water-skier wearing a football helmet laughs hysterically as he is towed through a fusillade of carp.
In Louisiana, Arkansas, Tennessee, and Missouri, Asian carp are now a familiar if irritating phenomenon. But as the fish have advanced—presently they’re as far north as Minnesota and as far east as Indiana—wildlife agencies and fishermen’s lobbies in the Great Lakes region have become alarmed. Commercial and sport fishing in the lakes is a $7.5 billion industry, and officials fear it will be ruined if the carp invade and take over. The flashpoint of the concern has been the Chicago Sanitary and Ship Canal, which connects the Illinois River to Lake Michigan. The U.S. Army Corps of Engineers installed heavy-duty electrical fish barriers on the canal, and the Illinois Department of Natural Resources poisoned the canal on two occasions, killing thousands of fish while turning up a single bighead carp. Downstream, fishermen hired by the government have pulled hundreds of tons of bigheads and silvers from the upper reaches of the Illinois.
The Army Corps maintains that the invasion of the Asian carp has been halted short of the Great Lakes. But are the electrical barriers a Maginot Line? In June 2010, a 19-pound bighead was caught in Calumet Lake, upstream of the barriers and only six miles from Lake Michigan. DNA traces of silver carp have also been detected in the waterways above the barriers. As a result, politicians outside of Illinois have demanded that the canal be shut. A lawsuit was filed by neighboring states, but an appeals court sided with Illinois last year, keeping the canal open for now.
