Graduate Program

Biological Sciences

Degree Name

Master of Science (MS)

Semester of Degree Completion

Summer 2022

Thesis Director

Robert E. Colombo

Thesis Committee Member

Scott J. Meiners

Thesis Committee Member

Eden L. Effert-Fanta


Despite the growing number of dam removals to date, very few have been studied to understand their impacts on stream fish communities. Despite being the most common type of dam in the U.S., an even smaller proportion of studies focus on the impacts of low-head dam removals, instead, focusing on the impacts of removal of larger dams. In this study, two previously impounded Illinois rivers were monitored to assess the impacts of low-head dam removal on the functional assemblage of stream fishes. This was accomplished by aggregating fishes into habitat and reproductive guilds, relating community changes to habitat, environmental metrics, and stream quality. Prior to removal, the slackwater guild was the most prevalent habitat guild throughout both rivers, while nest builders and benthic spawners were the most abundant reproductive guilds. Following removal, habitat conditions and fish assemblages improved throughout both rivers, with improvements in QHEI, IBI, water temperature, and dissolved oxygen, as well as a shift to more evenly distributed representation of both guild types. The improvements in environmental metrics and overall stream quality, particularly in the impounded habitats, indicate diminished habitat homogeneity, and a shift towards natural habitat diversity. This habitat diversification likely led to the restoration of a range of potential niches, thereby increasing the array of guild types that may inhabit these rivers, while simultaneously limiting single-guild dominance.