LimnoTech Inc.

Chicago waterway habitat case study


Courtesy of LimnoTech Inc.

Habitat study determines limiting factors to fish
The Chicago Area Waterway System (CAWS) is a network of 78 miles of rivers and deep-draft canals in and around the City of Chicago. The Metropolitan Water Reclamation District of Greater Chicago (MWRDGC) maintains the system for navigation, flood control, and wastewater conveyance. The CAWS is unique in that 75% of the system is manmade canals. A system of locks and dams controlling flow creates a completely artificial hydrologic regime that can vary dramatically during storm events.

The MWRDGC has spent millions of dollars on water quality improvement in the CAWS over the last three decades. When new dissolved oxygen water quality standards were recently proposed, they asked the question: given the apparent physical habitat limitations in the CAWS, will more restrictive standards really help fish in the system? To answer this question, MWRDGC commissioned LimnoTech to inventory physical habitat, determine the importance of physical habitat relative to water quality, and evaluate the potential for habitat improvement in the system.

LimnoTech conducted a comprehensive assessment of habitat and water quality in the CAWS that included physical habitat inventory; representative sampling of fish and macroinvertebrates; construction of a geo-database of habitat, biotic, and water quality data; development of a comprehensive geographic information system; development of a system-specific habitat index; and conceptual design of potential habitat improvement measures, focusing on the most limiting aspects of habitat in the system. To quantify biotic and habitat condition, LimnoTech developed both a CAWS-specific fish index and a CAWS-specific, non-wadeable habitat index, both of which underwent rigorous review by external experts.

LimnoTech found that physical habitat is more important to the resident fish than dissolved oxygen levels. We developed a comprehensive habitat index for a major urban waterway, something that had not been done on this scale before. This 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.

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