Assessment Comments
Assessment is based on results of an IDNR investigation of a fish kill in August 1999.
Basis for Assessment
SUMMARY: The Class B(CW) coldwater aquatic life uses are assessed (evaluated) as "partially supported.” These uses were assessed as "partially supported" for the 2000 through 2004 assessment cycles due to occurrence of a fish kill near Highlandville in 1999. Due to the absence of kills in at least three years following this kill, this assessment segment will be considered “evaluated.” Due to EPA uncertainty regarding the full recovery of the aquatic life in this stream subsequent to the kill, this stream segment will remain on Iowa’s 2006 Section 303(d) list (IR Category 5b). Fish consumption uses remain "not assessed."
EXPLANATION: Previous (2000, 2002, and 2004) assessments of the aquatic life uses were based on the occurrence of a fish kill on August 5, 1999, northwest of Highlandville in Winneshiek County. As stated in the assessment developed for the 2000 report, the kill followed a 2-3 inch rainfall event; no other water quality problems were observed. An estimated 3,200 fish were killed. No responsible party for the kill was identified.
The occurrence of a single pollutant-caused fish kill, or a fish kill of unknown origin, on a waterbody or waterbody reach during the most recent assessment period (2002-2005) indicates a severe stress to the aquatic community and suggests that the aquatic life uses should be assessed as “impaired”. If a cause of the kill is identified, and the cause is either known, or suspected, to be a “pollutant”, the assessment type is considered “monitored” and the affected waterbody is a candidate for Section 303(d) listing. Fish kills attributed to a pollutant, but where a source of the pollutant was not identified and/or where enforcement actions were not taken against the responsible party, will be placed into Integrated Report subcategory 5b. The intent of placing these waterbodies into Category 5 is not to necessarily require a TMDL but to keep the impairment highlighted due to the potential for similar future kills from the unaddressed causes and/or sources. For its draft 2006 assessment, IDNR considered this stream segment to be “not assessed” (IR Category 3a). According to IDNR’s assessment/listing methodology, if the most recent pollution-caused fish kill occurred on this stream segment more than six years ago (i.e., before the 2000-2005 period), any toxic impacts associated with the kill are assumed to have dissipated, and the assessment would thus not be included in the 2006 assessment/listing process. Due, however, to EPA uncertainty regarding the full recovery of the aquatic life in this stream subsequent to the kill, this stream segment will remain on Iowa’s 2006 Section 303(d) list (IR Category 5b).
Fish consumption uses are not assessed due to the lack of fish contaminant monitoring in this stream reach.
