Surveying the fish population: 50 years of MWRD data demonstrates resurgence, revitalization in area waterways

October 29, 2024

After 50 years of surveying fish activity in Chicago area waterways, Metropolitan Water Reclamation District of Greater Chicago (MWRD) scientists have observed a resurgent population of aquatic life.

MWRD Aquatic Biologist Erica Spiess and MWRD Principal Environmental Scientist Tom Minarik measure and weigh a largemouth bass pulled from the North Shore Channel near Touhy Avenue.

On a warm September morning with their boat tethered to a concrete pylon in the North Shore Channel under Touhy Avenue, a team of MWRD aquatic biologists pulled one fish after another for inspection, measurement, and weighing before releasing them back to their environment. Like a group of patients lining up for their physical examination, 700 fish were examined, representing 17 different species.

This year marks the 50th anniversary of the MWRD's fish monitoring program in the Chicago Area Waterway System (CAWS), and as water quality has improved over that time, the MWRD has noted a significant rise in fish populations. When the MWRD first began studying fish in 1974, they documented only 10 fish species. Today, the total number of fish species has risen to 77 in the CAWS. This includes more than 30 game fish species and 62 species that are native to Illinois. Additionally, the numbers of fish collected, also known as the catch rates, have steadily increased. For example, in the 1980s the MWRD collected an average of 104 fish per hour of electrofishing at the Touhy Avenue location on the North Shore Channel. That increased to 458 fish per hour in the 2010s.

"Today, the Chicago Area Waterway System is healthier than ever," said MWRD President Kari K. Steele. "Thanks to advancements in our treatment operations, the Tunnel and Reservoir Plan, stronger advocacy and strategic planning, and the support of local partners and landmark federal legislation like the Clean Water Act, the CAWS is thriving. Our water resources in Lake Michigan and the Chicago River are world-renowned."

MWRD aquatic biologists conduct fish monitoring periodically at 26 locations throughout its service area, which includes the Chicago, Calumet, and Des Plaines River Systems. Over 50 years, the MWRD has also returned on an almost annual basis to about 10 sites, including at Touhy Avenue where Lincolnwood, Skokie and Chicago converge. The biologists conduct their fish surveys on the CAWS using an active capture technique known as boat electrofishing where the boat's hull acts as a cathode, while the anodes are on the electrofishing booms which project from the front of the boat. The boat has an onboard generator that releases pulsed direct current electricity between the submerged cathode and anode. After the current goes into the water, the fish are briefly stunned, and MWRD staff collect them in nets to place in a tank before transferring them for processing. Once brought aboard, the scientists identify, inspect, and measure the length and weight of each fish.

MWRD staff patrol the Calumet River in October for an electrofishing survey where they pulled a variety of fish, including a bowfin. The MWRD monitors for fish at 26 locations throughout its service area, which includes the Chicago, Calumet, and Des Plaines River Systems.

In the North Shore Channel catch, there were dozens of gizzard shad, several 12-to-15-pound common carp, a few white suckers, several minnow species including golden shiners and fathead minnows, and hundreds of game fish like largemouth bass, bluegill and crappie. There were also a few invasive round goby fish that were collected and sent to the lab. Some of the smaller fish they could not immediately identify were also bottled up in formalin and sent to MWRD labs for processing.

Each fish is inspected by the aquatic biologist for any anomalies, and fortunately, most were healthy. They found a largemouth bass with a tag on it from a previous study, leading to future analysis and more understanding of the fish activity. The scientists make detailed notes and are on the lookout for invasive or endangered fish. The banded killifish, for example, is listed by the Illinois Department of Natural Resources as a state threatened species, yet MWRD aquatic biologists have been able to identify an increasing number of the banded killifish pulled from the CAWS.

The MWRD's 50 years of monitoring the species composition, distribution, and relative abundance of fish populations in the CAWS has proven to be a great tool that provides a visual aid to demonstrate the benefits of the MWRD's commitment to its mission to improve the water quality in its service area. Continued long-term monitoring is essential to further evaluate how fish populations and overall ecosystem health are changing over time and across different areas in response to ongoing water quality improvement efforts by the MWRD and other stakeholders.

MWRD aquatic biologists conduct electrofishing surveys throughout the year in the Chicago Area Waterway System to gain a better understanding of the health of the waterways. MWRD Aquatic Biologist Nick Kollias holds a common carp caught in the North Shore Channel. The common carp has long thrived in the Chicago Area Waterway System.

"When we began constructing more than 60 miles of local waterways more than a century ago, we were attempting to reverse the flow of the water so we could keep our drinking water and waterways safe. We provided drainage for the Chicago region and conveyed wastewater before wastewater treatment ever existed," said MWRD Vice President Patricia Theresa Flynn. "Now because of improved water quality, we are seeing not only more demand for the waterways but a thriving ecosystem of fish and other aquatic life living among us."

More information on the MWRD's fish monitoring can be found using the MWRD water quality mapping tool.