Biohavens – the only truly bio-mimicking floating wetland – Case Study #19 – Fish habitat

13 November 2015

Evaluating BioHaven Floating Islands as Fish Habitat in the Chicago River

Project Location: Chicago, Illinois USA

Masters student Joshua Yellin conducted a study on the Chicago River, listed as one of America’s most endangered rivers, which showed that floating treatment wetlands (FTWs) may provide enhanced fish habitat. FTWs used in the study were BioHaven floating islands donated by Floating Island International. This project was undertaken by Mr. Yellin as part of a Master of Science degree in Natural Resources and Environmental Sciences at the University of Illinois at Urbana-Champaign.


The Chicago River is a prime example of an urban watershed facing many anthropogenic pressures, including pollution, invasive species and habitat destruction or severe alteration. In 2011, American Rivers named it one of America’s ten most endangered rivers because 1.2 billion gallons of treated, but not disinfected, wastewater is dumped into the river every day. Another major problem is habitat destruction and alteration caused by Chicago’s development. Over the past 150 years, much of the river has been dredged and channelized to accommodate barges, allow for easy maintenance and prevent erosion. A challenge now is finding a practical solution to the loss of habitat.

Channelized rivers like the Chicago River have lower-quality fish assemblages than natural rivers, in large part because of low habitat heterogeneity. Floating treatment wetlands (FTWs) were proposed as a viable enrichment option for fish habitat. The question is, could FTWs provide better fish habitat than either open water or standard docks?

To assess the effectiveness of FTWs as fish habitat, this study used minnow traps to collect and compare fish species and abundance at three locations: underneath the FTW (the experiment), underneath a floating dock (a control) and in an unshaded area of the river (a second control). All three sites were in the same 100-meter stretch of the Chicago River (Figure 1).

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This study found fish to be present more frequently at the FTW (Figure 2) than at the dock, at a statistically significant level. Fish were caught in the subsurface FTW minnow traps on nine occasions, while fish were caught in the subsurface dock traps on only three occasions. The FTW minnow traps produced 2.04 fish per sampling event, while the dock traps produced 1.11 and the open water traps produced zero fish overall. These results imply that FTWs may be effective habitat for fish in the Chicago River, even more effective than other cover that is currently available to them.

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Possible reasons for the fish increase at FTWs include food supply, plant roots and water quality. First, the woven plastic of the FTW used in this study provided significantly more surface area for bacterial and algae growth than did the dock. This could have supplied a more abundant food supply that could be consumed directly by fish, or indirectly by supporting plankton and macroinvertebrates consumed by fish.

Second, plant roots growing underneath the FTW made it more structurally complex than the nearby dock. These roots also provided more surface area for periphyton, as well as a potential habitat and food source for fish, plankton and macroinvertebrates.

Third, water quality may have been improved under the FTW, which could have played a role in the presence of fish. Other studies have shown that FTWs are effective at improving water quality in rivers and other waterways.


  •   Fish were found significantly more often under the FTW than under the nearby dock.
  •   More fish were caught underneath the FTW than either under the dock or in open water.
  •   These results would appear to justify larger-scale research to demonstrate whether and why FTWs are a sufficient fish habitat solution in the Chicago River and elsewhere.

Yellin, J.M. (2014). Evaluating the Efficacy of an Artificial Floating Island as Fish Habitat in the Chicago River: A Pilot Study. Unpublished Master’s capstone project. University of Illinois, Urbana-Champaign.

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