Mud Lake Winter Fish Habitat Monitoring Planned
Posted: 03/06/2014
Hydrologists with the U.S. Army Corps of Engineers and Iowa DNR fisheries biologists are working to improve fish overwintering conditions in Mud Lake and Zollicoffer Slough, two historic overwintering areas near Dubuque. 

The lake and surrounding floodplain were submerged when Lock and Dam 11 was completed in the late 1930s and the increased connectivity with the main channel introduced current which did away with the backwater overwintering site.  A habitat rehabilitation and enhancement project (HREP) was completed there in 2006 to restore the backwater areas providing fish a refuge away from river channels.

The Mud Lake HREP constructed a deflection dike to re-establish connectivity more similar to the natural river conditions that supported fish overwintering.  Creating backwater habitat in the channel border was expected to re-establish fish overwintering by reducing current velocity and increasing temperatures without causing oxygen stress.  Construction began in April 2002 and was completed in August 2006.  Modifications to inlets were completed in 2006 when monitoring revealed excessive current velocity in the dredged channels. 

Additional monitoring using a dye trace will be used early next week (March 11) to determine location of current through the project area to enable managers to adjust the flow to better accommodate overwintering fish.  Material to further reduce the notch opening at Mud Lake was stockpiled on site in the event it would be needed at the completion of the study.    Ice anglers in the area may notice a red tint to the water if fishing downstream of the study area.  The dye quickly dissipates as it moves downstream and has no adverse effects on water quality, fish or wildlife.