The Illinois Department of Natural Resources and Friends of the Chicago River plan to release 30,000 catfish into the river as part of a habitat restoration project.
Friends of the Chicago River said the channel catfish will be released near Blue Island and a spot in downtown Chicago on Tuesday.
Eventually the group plans to release 100,000 catfish into the river and 400 structures known as nesting cavities to encourage the fish to repopulate the river.
Catfish numbers have been limited in the Chicago River for years.
The project is being paid for with a $300,000 grant from the National Fish and Wildlife Foundation.