Sweetwater Seas Under Siege - Part 4: The Chicago Barrier: Inside the Billion-Dollar Battle Against the Carp at the Continental Divide

The Sweetwater Seas Under Siege - Part 4: The Chicago Barrier: Inside the Billion-Dollar Battle Against the Carp at the Continental Divide

The first two waves of ecological catastrophe assaulted the Great Lakes through the St. Lawrence Seaway, the system’s “Front Door”. The sea lamprey and the alewife traveled this route. The zebra and quagga mussels followed, destroying the lakes’ food web from the bottom up. Now, the largest freshwater system faces a massive invasion brewing at its vulnerable “Back Door”: the manmade connection to the Mississippi River basin near Chicago. This threat comes from four species of large, voracious Asian carp. If these monster-sized fish succeed in colonizing the Great Lakes, some experts fear the region could be reduced to a “carp pond”.

The Destruction of the Divide

The words “continental divide” usually suggest a great mountain crest splitting water flow across North America. A similarly crucial continental divide once separated the Great Lakes watershed from the Mississippi River basin. This divide stretched across the western edge of downtown Chicago. For thousands of years, water on one side flowed south toward the Gulf of Mexico, and water on the other side flowed east toward the Atlantic Ocean. The Mississippi basin covers about 40 percent of the continental United States.

This natural barrier was finally destroyed in the mid-1800s. Early explorers, Father Jacques Marquette and Louis Joliet, noted a marshy shortcut between the basins in 1673. Opening this soft spot with a canal would create a nonstop navigation corridor from Lake Erie to the Gulf of Mexico. This ambitious plan was first realized with a relatively crude navigation channel in 1848.

The city of Chicago soon mushroomed. Its population grew from less than 5,000 in 1840 to more than 100,000 just a decade after the first canal opened. Chicago became the nation’s busiest port by 1869 due to the massive flow of cargo like grain, lumber, and livestock.

In the 1890s, Chicago undertook a far more audacious engineering feat. City leaders wanted to protect their drinking water, which they drew from Lake Michigan, despite also flushing sewage into it. Engineers designed the Chicago Sanitary and Ship Canal, which opened in 1900. This 25-foot-deep (7.6 m), rail-straight waterway reversed the flow of the Chicago River. The river formerly flowed into Lake Michigan, but now Lake Michigan water feeds the river. This river then flows into the canal, crosses the continental divide, and sends Chicago’s waste into the Des Plaines River, then the Illinois River, and ultimately into the Gulf of Mexico. This act preserved Chicago’s water source but created an unnatural connection between the two massive watersheds. The canal became the Great Lakes’ biological “Back Door”.

The Monster-Sized Newcomers

The invasion through this back door began not with a river herring, but with a radical new idea in weed control. In 1963, a station wagon delivered dozens of juvenile grass carp to an Arkansas federal research lab. These Asian natives were meant as a non-toxic alternative to chemical herbicides to clean fish farm ponds. A fish farmer accidentally imported three other species of Asian carp within a decade. These included black carp, which eat mollusks; and the filter-feeding bighead and silver carp.

Arkansas quickly sought an “elegant, if a bit repugnant,” plan to use these fish. Phase one involved planting bigheads and silvers in experimental sewage lagoons. The carp would convert decaying human waste into fish flesh. Phase two aimed to sell those fish as food to fund small cities’ sewage treatment costs. The federal Food and Drug Administration (FDA) quickly halted this plan.

The Asian carp soon escaped into the Mississippi River basin. Many believe former state hatchery workers let some go. Biologist Mike Freeze acknowledged that the bighead and silver carp that got loose likely escaped on his watch. Freeze said he is “old enough and big enough” to admit that he would change a lot of things in his life.

Once established, the filter-feeding bighead and silver carp reproduce prolifically and consume plankton aggressively. They can grow up to 70 pounds (31.8 kg) and eat up to 20 percent of their weight in plankton per day. This extreme consumption rate would destroy the Great Lakes food web, which is already struggling after the mussel invasions decimated its plankton foundation.

The silver carp are infamous for leaping grotesquely out of the water like “piscine missiles” when boat motors agitate them. Bighead carp lurk deeper, growing rapidly on the abundant nutrients. Commercial fisherman Orion Briney described the terrifying scale on the Illinois River. Briney can catch 15,000 pounds (6,804 kg) of bigheads in his nets in just 25 minutes. When asked if carp would thrive in the Great Lakes, Briney groaned, noting the lakes are hundreds of feet deep. He cautioned that by the time officials realized they had a problem, it would be “too late”.

The Electric Defense: A Costly Compromise

Congress recognized the threat nearly two decades ago. It authorized an experimental electrical fish barrier on the Chicago canal, about 35 miles (56.3 km) downstream from Lake Michigan. Underwater electric barriers had succeeded elsewhere, but never on a major navigation corridor like the Chicago canal. The initial barrier cost $1.5 million and became operational in 2002.

The experimental barrier was always intended as a Band-Aid until a more permanent solution could be devised. Congress then funded a much larger version, built to last decades and operate at four times the strength of the original.

The U.S. Coast Guard, whose primary mission is protecting barge workers, feared the current would cause sparks between barges carrying petroleum. Army Corps General John Peabody took charge of the carp fight in 2008. Peabody had led 3,000 engineers in Iraq and had a background in public administration. He was motivated by his childhood memories of the polluted Great Lakes and wanted to prevent a “calamity”.

Peabody eventually turned on the new barrier but compromised with the Coast Guard. The new barrier, designed to run as high as four volts per inch, was set at only one volt per inch, the same as the demonstration barrier. This voltage was safe for the barge industry but was not strong enough to stop juvenile fish.

Hunting the Invisible Enemy

The Army Corps lacked physical evidence that carp had reached the barrier area, despite tracking their northward migration. They knew nets were easy for the fish to avoid. Electroshocking devices were ineffective because the canal was too deep.

This is where science intervened. University of Notre Dame scientists, led by David Lodge, developed a new tool called environmental DNA (eDNA). This technique detects microscopic flecks of DNA shed by organisms into the water. eDNA samples are put into a test tube with engineered genetic markers, or primers, that attach only to the target species’ DNA. The sample is then heated and cooled repeatedly. This process, called replication, can multiply a single piece of DNA beyond a billion copies, causing the targeted DNA to glow under ultraviolet light.

By early 2009, Lodge’s team applied the eDNA test to the Chicago canal. They were trying to identify the “leading edge” of the invasion. The scientists had to move cautiously, knowing the technology was still new and unpublished in journals. The Army Corps gave the team permission to continue.

The team continued to find positive results farther north. In September 2009, they reported Asian carp DNA about 10 miles (16.1 km) farther upriver than the fish had ever been seen. This meant at least one carp had navigated the last lock before the electric barrier. General Peabody reacted by doubling the barrier voltage.

On November 18, 2009, Lodge sent an email notifying Army Corps officials of the worst possible news. Water samples beyond the barrier had tested positive for Asian carp DNA. Lodge recalled feeling “a little sick” when he hit the send button. DNA cannot drift upstream. A positive sample above the barrier meant at least some Asian carp had somehow passed through.

The Poisoning and the Single Fish

The news that the “last line of defense” had failed triggered widespread political alarm. Attorneys general from five Great Lakes states went to federal court to force the Army Corps to shut down the navigation locks near Chicago. They argued this was necessary to block the carp’s final advance into Lake Michigan.

Peabody’s team chose a different action. On December 3, 2009, the government poisoned a six-mile (9.7 km) stretch of the canal leading up to the barrier. This massive operation involved 400 federal, state, and Canadian fishery workers. The goal was to “sterilize” the canal because the new barrier required a temporary shutdown for maintenance.

The poisoning was likened to “chemotherapy” by President Obama’s Great Lakes Czar, Cameron Davis. Thousands of fish died, but no Asian carp surfaced. Finally, at 7 p.m., after more than 54,000 pounds (24,494 kg) of carcasses were collected, officials announced they had found a single 22-inch (56 cm) bighead carp. This confirmed that the carp were indeed in the poisoned stretch just below the barrier.

The controversy over the eDNA evidence persisted. In late May 2010, the government conducted a second poisoning just six miles (9.7 km) from the Lake Michigan shoreline. This area had repeatedly tested positive for Asian carp DNA. The second poisoning claimed another 100,000 pounds (45,359 kg) of fish. Yet, again, not a single Asian carp was found.

A month later, on June 23, 2010, irrefutable physical proof arrived. The Illinois Department of Natural Resources announced that a 20-pound (9.1 kg) adult bighead carp had been caught in a net above the barrier. This was just six miles (9.7 km) from the Lake Michigan shoreline. This capture grimly validated the scientists’ eDNA findings.

The Army Corps immediately sought to downplay the breach. Officials claimed lab analysis of the fish’s ear bones “suggest[ed] to us that the fish . . . may have been put there by humans”. They cited rumors of “cultural releases” by people of Asian ancestry. However, an independent reviewer warned that no definitive conclusion could be reached based on the ear bone analysis.

The Price of a Permanent Solution

The capture of the fish above the barrier pushed the neighboring states’ legal fight forward. The lawsuit aimed to force the Army Corps to expedite a study on permanently plugging the canal and reconstructing the divide.

The Army Corps released its study in 2014. The 10,000-page plan concluded that plugging the canal would cost up to $18 billion. Critics quickly dismissed this figure as vastly inflated and containing unrelated projects. The agency included $12 billion for new reservoirs, sewer tunnels, and sediment removal. These are “worthy projects” but are not directly required to stop the fish. Critics saw this as a cynical ploy to make the project unappealingly expensive.

Henry Henderson, former environment commissioner for Chicago, stated the study could be read as “a laundry list of why this can’t be done”. An independent engineering study, funded by a group representing Great Lakes mayors and governors, concluded the barrier could be built for as little as $4.25 billion.

Opponents of plugging the canal, particularly the barge industry, remain confident the plan will fail. Mark Biel, an industry advocate, believes the high cost, legal hurdles, and political resistance to sending treated wastewater back into Lake Michigan will kill the idea. Biel is confident the permanent barrier will not happen in his lifetime.

A Shaky Defense

The political and financial disputes mean the electric barrier remains the only active defense against the carp. Since 2009, the federal government has spent more than $318 million to block the carp. Yet, the defense is precarious.

In early 2014, underwater video revealed dozens of little fish swimming upstream through the electrified water. Lab tests had previously claimed this was impossible at the barrier’s operating voltage. While the fish species cannot be identified, the breach proves the barrier is imperfect.

The DNA evidence continues to mount. Asian carp DNA turned up in Wisconsin’s Door Peninsula, 200 miles (321.9 km) north of Chicago, in 2013. It was also detected in the Chicago River just a block from the Lake Michigan shoreline in 2014. This genetic “smoke” suggests live fish are present.

Biologists argue that relying solely on traditional methods, like nets and poisons, is dangerous. Asian carp tend to sink when poisoned in cold water. They are adept at avoiding nets. Ecologist David Lodge compared relying on old tools to trying to detect cancer with a physical exam when an MRI is available.

The danger of hidden carp populations is clear. A tiny private fishing pond in Missouri, stocked only with bass and catfish, suddenly saw its fish starving. When the owner poisoned the pond, the rotting carcasses of about 300 bighead carp surfaced. The fish, some up to 35 pounds (15.9 kg), had flourished invisibly for a decade. This highlights how easily these huge, aggressive feeders could dominate the vast, deep expanses of the Great Lakes without being noticed until catastrophic ecological damage is complete.

The Asian carp, black carp, presents a specific irony. This species eats mollusks. It could theoretically eat the invasive zebra mussels that have ravaged the Great Lakes food web. However, black carp are also massive and could introduce yet another unpredictable layer of chaos into the already synthetic Great Lakes ecosystem. The choice remains between spending billions to rebuild nature’s original dividing line or accepting eternal war against the invasive species flooding through both the front and back doors.