Assessment Comments
Assessment remains based on results of an IDNR investigation of a fish kill in August 2004.
Basis for Assessment
[Note Prior to the 2008 Section 305(b) cycle, this stream segment was classified only for general uses. Due to changes in Iowa’s surface water classification that were approved by U.S. EPA in February 2008 (see http://www.iowadnr.gov/Portals/idnr/uploads/water/standards/files/swcdoc2.pdf), this segment is now presumptively designated for Class A1 (primary contact recreation) uses and for Class B(WW1) aquatic life uses. According to the Iowa Water Quality Standards, all perennial rivers and streams and all intermittent streams with perennial pools that are not specifically listed in the Iowa surface water classification are designated as Class A1 and Class B(WW1) waters. Thus, for the current (2012) assessment, perennial flow is presumed, and the available water quality monitoring data will be compared to the applicable Class A1 and Class B(WW1) water quality criteria.]
SUMMARY: The presumptive Class A1 (primary contact recreation) uses remain "not assessed" due to a lack of water quality information upon which to base an assessment. The presumptive Class B(WW-1) aquatic life uses remain assessed (evaluated) as “partially supported” (IR Category 5b) due to a fish kill in August 2004. Although a definitive cause of the kill was not identified, IDNR investigators hypothesized that feedlot runoff may have been involved in the kill. The party responsible for the kill was not identified. This impairment is appropriate for Category 5b of Iowa’s Integrated Report (=Section 303(d) list). Due to the age of the assessment information (greater than five years), the assessment type is changed from a higher confidence (“monitored”) assessment to a lower confidence (“evaluated”) assessment.
EXPLANATION: This kill occurred on or before August 25, 2004. A definitive cause of the kill was not identified. The kill began south of Marcus at a bridge on the north side of section 26 of T92N, R42W; the kill extended 5.3 miles downstream and ended in the center of Section 10 of T91N ,R42W, Cherokee County. An estimated 7,201 fish were killed; no estimate of the value of the fish killed was provided. The fish killed included non-game species (e.g., minnows, suckers, and darters) and also included approximately 2,000 stonecats (Noturus flavus). No responsible party was identified. Although a definitive cause was not identified, IDNR investigators hypothesized that runoff from nearby sheep feedlot may have caused the kill.
According to IDNR’s assessment/listing methodology, 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 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 previous assessment/listing cycles, IDNR had considered fish kill-impaired (IR 5b) waters with no subsequent kills in the three year subsequent to the kill as appropriate for de-listing and for movement to IR categories 2b or 3b (i.e., Iowa’s list of waters in need of further investigation). Due, however, to EPA uncertainty regarding the full recovery of the aquatic life following the kill, any existing fish kill (5b) impairment will remain in IR Category 5b until more recent monitoring has shown full recovery of the aquatic communities affected by the kill. Thus, this assessment segment will remain in Category 5b of Iowa’s Integrated Report.
