Illinois removed dams from Brewster Creek in 2006; by 2014, surveys had found 14 fish species not previously recorded in the restored stretch, including catfish

For years, aquatic species moving through Brewster Creek encountered an obstacle they could not pass. However, after the barriers began disappearing in 2006, previously blocked species started returning to the restored section. In 2006, the state of Illinois completed the removal of multiple dams on Brewster Creek, restoring a continuous stream channel. The results became increasingly visible over the following years. The National Oceanic and Atmospheric Administration (NOAA) report revealed that by the year 2014, surveys found 14 fish species in the repaired area for the very first time, such as channel catfish, flathead catfish, minnows, and darters. The project also noted important migrations of fish like smallmouth bass and quillback as some of the earliest fish to migrate into the newly connected channel.

How engineers restored a blocked waterway

Instead of demolishing the structures all at once, the engineers came up with a plan to remove them in stages. This enabled Brewster Creek to acclimate itself a bit at a time and to minimize the likelihood of downstream sediment releases. “Results of the project showed that the stream had found its own natural channel through the former impoundment through a gradual approach. One concern with dam removal is sudden sediment movement downstream. Researchers found that the phased approach allowed sediment changes to occur gradually rather than causing a major disruption. The restored channel was also left in a natural state as opposed to being heavily engineered, allowing scientists to see how the creek responded after the barriers were removed.


Fish returned sooner than expected

One of the first signs of recovery came from the fish themselves. Their early return provided evidence that the restored channel had reconnected habitats that were previously inaccessible. Their arrival indicated that species living below the former barriers were able to reach habitat that had previously been inaccessible. There was a greater change after long-term monitoring. Some of these included channel catfish and flathead catfish, which were not previously documented before restoration. Several other species of darters and minnows were also present, adding to the variety of fish in the creek.

The long-term monitoring that revealed change

The project was not completed after the last section of the dam was removed. Fisheries biologists have continued to monitor Brewster Creek to learn about how the ecosystem changed over time. Fish surveys were conducted to count fish species and biological condition changes. Long-term monitoring showed that fish diversity increased after the dam removal, with surveys recording species that had not previously been documented in the restored reach. These repeated surveys enabled researchers to differentiate between temporary change and long-term recovery, and gave one of the most comprehensive records of fish community response to barrier removal in the region.

Why Brewster Creek became an important restoration project

The Brewster Creek project was part of a larger program to link disconnected waterways throughout the northeast region of Illinois. At the time of the NOAA evaluation, 20 dam removals and four fish-passage projects were completed in the region since 1998. Brewster Creek was one of the sites chosen as an example because changes in the physical structure of the stream and biological responses to changes in fish populations could be documented over several years. The NOAA evaluation suggested that the phased removal approach at Brewster Creek did not produce the major downstream impacts that researchers were monitoring for. At Brewster Creek, researchers observed that the phased approach allowed the stream to recover while maintaining stable sediment movement and water quality.

The ongoing evolution of a restored waterway

The removal of the dams did not immediately return Brewster Creek to a stable form. Researchers persisted in recording changes in the resurgent reach long after fish had started to recolonise it. A knickpoint was observed to travel upstream, a process involving a steep change in the channel where the new stream path eroded through accumulated reservoir sediment. The knickpoint moved approximately 277 metres in 2006, gradually cutting a meandering channel through the former lakebed. The observations extended well beyond Brewster Creek itself. The data collected from the site were used to examine how streams respond over time after barriers are removed.