Roller Mill Dam Story and the Results of Five Years of Monitoring Since Dam Failure on the Middle Bark River Southeastern Wisconsin

In June 2008, high water on the Middle Bark River, Waukesha County, Wisconsin, caused Roller Mill Dam to partially fail. The dam was in the process of abandonment during the failure, options for removal were evaluated over a five-year period with removal occurring in late 2013. Resource managers expressed concern that changes in the hydrology of the river may impact the existing twenty six native fish species, including the state Endangered slender madtom (Noturus exilis) as well as the state Special Concern least darter (Etheostoma microperca) and weed shiner (Notropis texanus).  Annual electrofishing collections and macroinvertebrate kick-samples above and below the dam allowed evaluation of the river’s biota as the river adjusted to removal of the dam.  The Fish Biotic Index (FBI) and macroinvertebrate based Hilsenhoff Biotic Index (HBI) remained surprisingly consistent throughout these hydrological changes. During five years of sampling the FBI ranged from 40 to 45 above the dam and 50 to 62 below the dam on a 0-100 scale with higher numbers indicating better quality.  The HBI ranged from 4.67 to 5.23 above the dam and 4.94 to 5.28 below the dam on a 1-10 scale with lower numbers indicating higher quality.  No annual trend was noted.