Scientists Discover Record Smallmouth Bass in Cal-Sag Channel

UPDATE: In a groundbreaking discovery, scientists from the Metropolitan Water Reclamation District (MWRD) announced the capture of a record-breaking smallmouth bass weighing 3.9 pounds and measuring 19.7 inches in the Cal-Sag Channel. This remarkable find, made on October 30, 2025, marks the first of its kind in over 51 years of fish monitoring in the Chicago Area Waterway System, showcasing the area’s significant improvement in water quality.

Environmental research technician Mike Ress, who led the discovery alongside colleague Mike Portala, expressed astonishment at the transformation of the once-polluted waterway. “This is something I never really expected based on the hearsay I’ve been hearing my whole life,” Ress stated, emphasizing the vibrant ecosystem now thriving in the channel, which includes various fish species and herons.

The Cal-Sag Channel, stretching 16 miles, historically suffered from severe pollution due to human waste and inadequate regulations. MWRD’s principal environmental scientist, Thomas Minarik, noted that finding any fish in the waterway was nearly impossible just 50 years ago. Back then, the water quality was so poor that only 10 fish species were documented during initial surveys. Today, that number has surged to 77 species, with catch rates skyrocketing from an average of 22 fish per hour in the 1970s to an astonishing 436 fish per hour in the 2010s.

The MWRD highlights that the increasing presence of sensitive game fish like the smallmouth bass indicates improved water conditions necessary for their growth. This significant ecological change can be attributed to a series of regulatory reforms and advanced water treatment technologies implemented over the decades. The construction of a tunnel and reservoir system in the 1970s greatly reduced sewage overflow incidents, enhancing water quality and providing a healthier habitat for aquatic life.

Minarik explained, “When you have a combined sewage overflow, that brings in a lot of pollutants into the system, which consumes dissolved oxygen and creates a stressful environment for fish.” The introduction of aeration stations in the 1990s has also played a crucial role in increasing oxygen levels in the water, enabling fish populations to thrive.

The record-breaking bass was discovered near the elevated pool aeration station in Blue Island, a site known for its community gatherings like the annual Blessing of the Waters. Event founder Tom Shepherd remarked on the broader implications of this ecological milestone, linking water health to community and wildlife well-being. “Water is our life; it’s as important as our blood that flows in our veins,” Shepherd said, underscoring the interconnectedness of the ecosystem.

Residents and wildlife enthusiasts are encouraged to engage with MWRD’s upcoming virtual tours starting on January 14, allowing participants to explore the history of Chicago’s waterways and the advancements in wastewater treatment technology.

As scientists continue to monitor and improve the health of the Cal-Sag Channel, this discovery serves as a beacon of hope for environmental recovery, showcasing the power of dedicated efforts to restore and protect vital ecosystems. Stay tuned for more updates on this developing story as MWRD continues its vital work in the region.