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Healthier Waterways Increased Fish Diversity in Chicago

New Research Shows Improvements to Management and Treatment Increases Water Quality and Biodiversity

February 23, 2022

Researcher on a boat in a body of water inspecting a container of water for larval fish.

Photo by: Shedd Aquarium/Brenna Hernandez

New research, led by Shedd Aquarium and published today in Science of the Total Environment, confirmed that efforts to reduce contaminants and improve water quality in the Chicago Area Waterway System (CAWS) correlate with increases in fish diversity in waterways like the Chicago River and Calumet River systems. While previous studies by Shedd and the Metropolitan Water Reclamation District of Greater Chicago (MWRD) found more fish species and increases in fish diversity, this research shows that the improvements to wastewater handling and treatment directly led to these important fish recoveries in the local waterways. Together, policy and water management strategies continue to increase the health of Chicago’s waterways, which serve as a critical economic, recreational and cultural asset to the city and subsequently create environments conducive for aquatic life.

“While urban freshwater systems represent some of the most vulnerable environments, this study showcases how improvements to infrastructure can benefit the whole ecosystem, including for the animals that call it home,” said Dr. Austin Happel, research biologist at Shedd Aquarium and lead author of the study. “This is a positive sign for our local waterways because increases in the number of fish species means healthier ecosystems, which in turn means healthier communities and economies that rely on them.”

Happel analyzed this long-term data set to gauge how fishes in Chicago’s rivers are responding to actions taken to improve water quality. He reviewed a fish data set that consists of 483 samples from nine locations over 35 years collected by MWRD, paired with water quality data from the same locations and weather data for the Chicago area.

“We’ve continued to make significant investments and implement actions to increase the quality of the Chicago Area Waterway System, which includes over 76 miles of navigable waterways and connects the Great Lakes with the Gulf of Mexico,” said Dustin Gallagher, associate aquatic biologist at the MWRD and co-author of the study. “It is valuable for us to collect data and monitor this critical freshwater environment to understand the implications of advancements to the water treatment operations in our waterways.”

Since the enactment of the Clean Water Act 50 years ago, the MWRD has made several alterations to the storm and sewer water management systems integrated with the CAWS to enhance water quality. One significant effort is the Tunnel and Reservoir Plan (TARP), which is designed to reduce flooding and pollution caused by sewer overflows. The study showed the TARP has eliminated combined sewer overflow (CSO) events in sections of the CAWS and reduced their occurrence in others. Monitoring and assessing ecosystem responses to such changing conditions is a primary step in identifying shifts and will help manage and enhance urban waterways in the future.

“While improvements to water quality represent a great engineering and legislative achievement, the effects of climate change, including increased rainfall events and harsher winter conditions, threaten to halt or even reverse such improvements,” said Happel. “This growing understanding can inform where to focus mitigation strategies for the future. In the meantime, it is valuable for people to connect with their local waterways and hopefully become more invested in their future.”

Shedd Aquarium offers opportunities to paddle along the North Branch of the Chicago River guided by a Shedd nature expert during its Kayak for Conservation program each summer. The program is part of an ongoing commitment to improving access to nature for the public and connecting Chicagoans to the Chicago River ecosystem to foster a community dedicated to restoring and protecting it. In addition, people can sign up for an exclusive email, Surge, to receive knowledge and tools to take actions in daily life and tackle issues, including climate change, access to nature, pollution and more. Residents in the Chicago region can also learn more about conserving water during Overflow Action Days promoted by MWRD when weather forecasts predict significant rain.

To read the published research study, “Decreases in wastewater pollutants increased fish diversity of Chicago’s waterways,” visit

For more information about Shedd Aquarium’s research on the Chicago River, visit Shedd’s website here.

VISUALS: High resolution visuals of Shedd’s work on the Chicago River are available for preview and download here:
Credit: ©Shedd Aquarium