USE OF A CONTIGUOUS BACKWATER LAKE (SWAN LAKE) BY FISHES FOR
OVERWINTER HABITAT.

John H. Chick1, John K. Tucker1, Charles Theiling2, and Robert J. Maher3.  
1Illinois Natural History Survey, Great Rivers Field Station, Brighton, IL 62012  2U.S.
Geological Survey, Upper Midwest Environmental Sciences Center, LaCrosse, WI 54603 
3Illinois Department of Natural Resources, Brighton, IL 62012. 

Swan Lake is a 1200 ha backwater lake on the lower Illinois River that was created as a result of
the construction of Lock and Dam 26.  Sedimentation rates within the lake are high and have
affected aquatic habitats through reduced water depth and the formation of flocculent sediments
which reduce the coverage of aquatic plants.  As a result, the Army Corps of Engineers devised a
habitat rehabilitation project (HREP) to improve aquatic habitat within the lake.  Connection
between Swan Lake and the Illinois River are now managed with water control structures and the
lake has been subdivided into three independently managed units.  Prior to HREP construction,
the upper portion of the lake was maintained as a moist soil unit for migratory water fowl, and
will continue to be managed in this way.  Management of the middle unit will promote the
growth of aquatic vegetation for benefit of water fowl, and the lower portion will be managed for
fish and will maintain a connection to the lower Illinois river throughout most of the year.  In
1992, before construction of the HREP structures, a twelve month sampling project was
undertaken to help assess how the HREP might affect biological and physical characteristics of
the lake.  Fish sampling was an important part of this project, and demonstrated that abundance
of several fishes, including bluegill, black crappie, white crappie, bigmouth buffalo, and black
buffalo, increased substantially in the lower and middle portion of Swan Lake during the winter. 
This suggests that these areas are important overwinter habitats for fishes in the lower Illinois
and Mississippi Rivers.  Nevertheless, some differences were apparent in use of the lower and
middle portion of Swan Lake during the winter, suggesting that habitat quality for overwintering
fishes varies spatially.  Post-project sampling effort is scheduled to take place in 2002 to assess
changes in water quality, vegetation, invertebrates, and fishes.

Keywords: fish, overwinter habitat, Swan Lake, habitat rehabilitation project, Illinois River