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A view down the Chicago river, lined with greenery and with skyscrapers in the distance.

Along the walled bank of the North Branch of the Chicago River, new (foreground) and established artificial floating islands provide habitat where fishes can find food and spawn.

Historic changes in fish assemblages and water quality

The Chicago Area Waterway System (CAWS) represents a set of rivers whose flows have been reversed through a series of canals and are tied to the wastewater transport and treatment facilities of the area. Since the Clean Water Act was enacted in 1972, fish communities and water quality in the CAWS have been monitored by the Metropolitan Water Reclamation District of Greater Chicago (MWRD). In partnership with MWRD, Shedd research biologist Austin Happel, Ph.D., is analyzing this long-term data set to gauge how the fishes in Chicago’s rivers are responding to actions taken to improve water quality.

Staff and volunteers push the sections of a floating island off a pier and into the river

Planted floating islands, being launched by Shedd staff members, are made of coconut coir mats tied together with recycled plastic. The native wetland plants’ roots grow into the water, adding oxygen and providing habitat for fishes as well as their zooplankton prey.

If you restore it, will they come?

Restoration efforts vary across waterways, from removing dams to establishing new vegetation, and the potency of these actions also varies and can take years to be realized. Happel is looking at what effects restoration projects have on aquatic communities. For example, the Chicago River’s “Wild Mile” project represents a revitalization of a section of the North Branch of the industrial waterway using artificial floating islands, which may provide shelter and food for fishes while improving water quality. By studying the effects these various restoration efforts have on aquatic organisms, Happel can help others argue for similar actions in their areas.

A man sits at a bench in the dark, his headlamp illuminating a pan of water in front of him

Shedd research biologist Austin Happel examines the collecting tray of a light trap set at night amid the floating islands to attract larval fishes.

A closeup of a tiny larval fish swimming in a shallow pan of water

A tiny fish is evidence that some fishes are using the floating islands for spawning. Happel will compare what he finds with historic fish population records as well as track what species spawn as the islands grow out and are added to.


While fishes might be present in a waterway, finding a baby, or larval, fish means much more is going on below the surface. Not only are adults present, but there are also enough of them to find each other, they have appropriate habitat, enough food and suitable water quality to thrive and the egg produced from spawning survived through hatching, a milestone many fishes don’t pass. Thus, finding a larval fish is a revealing event. By looking at when and where fish are spawning, Happel can begin to assess where fish populations are thriving and where they may need attention.

“It’s exciting to see just how many fish species call Chicago home, and there is just so much we don’t know about what city life is like for them.”

Austin Happel, Ph.D., research biologist

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