Dramatic Recovery of Illinois Sport Fish Traced to Clean Water Act

Researchers from the Illinois Natural History Survey have surveyed fish in the Illinois River since 1957. Here, the team uses electricity to stun the fish for capture. (Aaron Yetter / Illinois Natural History Survey)Researchers from the Illinois Natural History Survey have surveyed fish in the Illinois River since 1957. Here, the team uses electricity to stun the fish for capture. (Aaron Yetter / Illinois Natural History Survey)

Conditions in the Illinois River near Chicago were so bad in 1972 that they had an eye-popping effect – literally.

The river had for decades received large amounts of Chicago’s untreated human and animal waste, causing a surge in sewage-related nutrients that depleted the water’s oxygen. Hydrogen sulfide gas bubbled to the surface, bringing up rafts of sewage fungus and other decaying matter.

“Back then, the only fish we were picking up were carp and goldfish, and it was awful seeing these fish,” said Richard Sparks, an aquatic ecologist with the Illinois Natural History Survey, in a press release. “They had tumors; they had eroded fins. They had various diseases, including what was called ‘pop-eye disease,’ where the eyes enlarged and just fell out of their eye sockets.”

Sparks is co-author of a new study documenting the remarkable recovery of largemouth bass, bluegill, catfish and other sport fish in the Illinois River. The species’ resurgence, from populations close to zero near Chicago through much of the 20th century to record levels now, began just after implementation of the federal Clean Water Act, according to the study by INHS, a division of the Prairie Research Institute at the University of Illinois.

In 1957, scientists set up a series of fish-monitoring stations in the Illinois River. Eventually, stations were added so that sampling extended from near Chicago all the way downstream to the Mississippi River. (Map by Danielle Ruffatto / Illinois Natural History Survey)In 1957, scientists set up a series of fish-monitoring stations in the Illinois River. Eventually, stations were added so that sampling extended from near Chicago all the way downstream to the Mississippi River. (Map by Danielle Ruffatto / Illinois Natural History Survey)

In 1972, Sparks began studying fish in the Illinois River, which had been one of the most productive waterways for commercial fishing in the Mississippi Valley until it began receiving Chicago’s untreated sewage at the start of the century.

That same year (1972), Congress passed the Clean Water Act, which provided the regulatory framework and funding to develop infrastructure to capture and treat stormwater and sewage. Since then, more than $3 billion has been spent to construct a massive network of reservoirs and tunnels in and under Chicago to capture the city’s vast outpouring of sewage and stormwater runoff.

Starting in the late 1980s and continuing into the 21st century, populations of 13 sport fish species – including bluegill, catfish, crappie, largemouth bass, sunfish and walleye – increased dramatically in the Illinois River, according to the new study, published Wednesday in the journal BioScience.

Populations of sportfish like walleye, pictured here, have increased dramatically in the Illinois River since the late 1980s, when the first changes under the federal Clean Water Act began to be implemented. (Josh Brugge / Illinois Natural History Survey)Populations of sportfish like walleye, pictured here, have increased dramatically in the Illinois River since the late 1980s, when the first changes under the federal Clean Water Act began to be implemented. (Josh Brugge / Illinois Natural History Survey)

Between 100 and 300 fish are now caught every hour in areas of the river close to Chicago, where in the 1950s and ‘60s, almost none were being caught, said Daniel Gibson-Reinemer, INHS fish biologist and lead author of the study.

“The closer it was to the [Chicago Sanitary and Ship Canal], the more dramatic the improvement was,” Gibson-Reinemer said. “As a biologist who has studied things in different rivers, you almost never see results like that when you’re looking at rivers. These types of positive changes almost never happen.”

Researchers found that the rebound of fish populations in the river parallels reductions in nitrogen pollution and sewage and improvements in water quality – all of which began with implementation of the Clean Water Act. 

“I think we kind of had an idea [about the recovery],” Gibson-Reinemer said. “But it wasn’t until we really started grasping the data until we could see how big it was.”

Despite the comeback story, the study notes that sport fish in Illinois still face significant threats. Invasive Asian carp, for example, are multiplying and consuming zooplankton, a primary food source for young sport fish and other species. Hormone-disrupting chemicals are also leaching into rivers from industrial and municipal sources.

“What the river went through in the 20th century, it was an enormous hurdle to overcome,” said Gibson-Reinemer, adding that he is troubled by ongoing efforts to weaken or sidestep the Clean Water Act. “In some ways, I worry that when we have improvements, we might take it for granted and don’t realize just how bad things were.”

The research team behind the study also included researchers from the U.S. Fish and Wildlife Service and the Illinois Department of Natural Resources.

Contact Alex Ruppenthal: @arupp aruppenthal@wttw.com | (773) 509-5623


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