Study Highlights How Sewage Overflows Disrupt Chicago River Ecosystem.

A recent study published in Knowledge and Management of Aquatic Ecosystems has uncovered significant ecological changes in the Chicago River following the release of untreated wastewater during heavy rainfall. The research, conducted by scientists at Shedd Aquarium, highlights how combined sewage overflows (CSOs) during storms disrupt freshwater ecosystems, particularly affecting zooplankton communities in areas like Bubbly Creek.

Chicago’s sewer infrastructure combines wastewater and stormwater in a single system. When intense rainfall exceeds system capacity, it triggers a CSO—redirecting untreated water into the river to prevent urban flooding. In July 2023, a series of storms led to the discharge of approximately 12.3 billion liters of untreated wastewater and stormwater into the Chicago River. Bubbly Creek, part of the river’s South Branch, received the bulk of this volume—about 9.1 billion liters.

Throughout the summer, researchers from Shedd Aquarium gathered water samples from multiple locations along the river to observe changes in zooplankton populations and water quality. Their findings revealed a striking shift: one zooplankton group, Chydoridae, nearly vanished from Bubbly Creek, while two others—Cyclopoida and Moinidae—saw significant population spikes.

"Any time human activity disrupts a natural system, it's cause for concern," said Dr. Austin Happel, lead author of the study and a research biologist at Shedd Aquarium. "Our research adds to growing evidence that CSOs pose serious ecological risks to urban waterways like the Chicago River."

Zooplankton, though small and often overlooked, play a vital role in aquatic ecosystems. Feeding on phytoplankton, they form a crucial part of the food web that sustains many fish species. Abrupt changes in their populations can signal broader ecological disturbances and potentially introduce harmful chemicals into the aquatic food chain.

The CSO event also had lasting impacts on water quality in Bubbly Creek. Shedd researchers reported a dramatic drop in oxygen levels—nearly reaching zero—along with elevated nitrogen concentrations. These changes drove fish away from the area for weeks, as confirmed by the aquarium’s acoustic telemetry monitoring program.

"As climate change brings more frequent and severe storms, understanding how CSOs affect our rivers is essential," Dr. Happel emphasized. "The Chicago River remains a biodiverse urban habitat, and protecting it is a shared responsibility."

To mitigate CSO impacts, residents are encouraged to conserve water during storms by delaying laundry and dishwashing, and reducing shower times. Homeowners can also disconnect downspouts from the sewer system, directing runoff into gardens instead. Additionally, Shedd Aquarium is partnering with local organizations to restore the South Branch of the river through community engagement, environmental education, and the creation of floating wetlands that provide refuge for wildlife.

Source:https://phys.org/news/2025-05-reveals-impact-sewage-chicago-river.html

This is non-financial/medical advice and made using AI so could be wrong.