Chicago Area Waterway System, Chicago, Illinois
Metropolitan Water Reclamation District of Greater Chicago
The MWRDGC maintains the CAWS for navigation, flood control, and wastewater conveyance. When new dissolved oxygen water quality standards were proposed, MWRDGC asked the question, “Given the apparent physical habitat limitations in the CAWS, will more restrictive standards really help fish in the system?” LimnoTech helped MWRDGC answer this question by conducting an extensive assessment of water quality and habitat in the CAWS.
Existing habitat assessment tools were not applicable to this unique, large-scale, urban system where most of the CAWS network is made up of manmade canals, nearly all of its water is secondary effluent, and a system of locks and dams creates a completely artificial hydrologic regime. We were able to overcome this limitation by developing and applying CAWS-specific fish and non-wadeable habitat indices, something that had not been done before at this scale. Our work included a physical habitat inventory; representative sampling of fish and macroinvertebrates; and construction of a geodatabase and GIS for water quality, biotic, and habitat data. We also applied advanced data analysis methods, including principle components analysis (PCA), multiple linear regression, and classification and regression tree (CART) analysis to identify the most significant physical habitat attributes in the system. Our work also involved a rigorous peer review by external experts.
We found that physical habitat is more important to the fish than dissolved oxygen levels. The habitat index allowed us to identify the most limiting habitat attributes, which informed conceptualization of habitat improvement measures. We also determined that if the system is to continue to serve its primary uses, improvements may not result in measurable improvements in the fish community.