Assessment Comments
Assessment remains based on results of a fish kill investigation in August 2008. Although assessed as potentially impaired for the 2010 Integrated Reporting cycle (IR Category 3b), subsequent review suggests that this fish kill was caused by a pollutant. Thus, this assessment was moved to IR Category 5b (impaired) of Iowa's 2012 Integrated Report.
Basis for Assessment
[Note: Prior to the 2008 Section 305(b) cycle, this stream segment was designated only for Class B(LR) aquatic life uses. Due to changes in Iowa’s surface water classification that were approved by U.S. EPA in February 2008, and due to the completion of a Use Attainability Analysis in 2007, this segment is now designated for Class A1 (primary contact recreation) uses. The stream remains designated for aquatic life uses (now termed Class B(WW2) aquatic life uses). Thus, for the current (2014) assessment, the available water quality monitoring data will be compared to the applicable Class A1 and Class B(WW2) water quality criteria.]
SUMMARY: The presumptive Class A1 (primary contact recreation) uses remain “not assessed” (IR 3a) due to lack of information upon which to base an assessment. The Class B(WW2) (aquatic life) uses remain assessed (evaluated) as "partially supported" (IR Category 5b) based on results of a fish kill investigation in August 2008.
EXPLANATION: The kill occurred on or before August 20, 2008. The kill killed 76,292 fish along 2.5 miles of the East Fork of the Wapsipinicon River. The value of the fish was estimated to be $40,053.15. No cause for the kill was identified. Water samples were collected at the time of the kill that ruled out livestock manure as the source of 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 (2006-2009) 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 was not identified during the IDNR investigation, or if the kill was attributed to non-pollutant causes (e.g., winterkill), the assessment type will be considered “evaluated.” Such assessments, although suitable for Section 305(b) reporting, lack the degree of confidence to support addition to the state Section 303(d) list of impaired waters (IR Category 5). Due, however, to the extremely large number of fish killed (~75,000), the length of the kill (2.5 miles), and the lack of environmental extremes during summer 2008 that would have contributed to this kill (e.g., low stream flow and/or high water temperatures), some type of pollutant cause is suspected. Thus, this assessment was moved from Category 3b of Iowa's 2010 Integrated Report (potentially impaired) to IR Category 5b (impaired) of the 2012 IR. This assessment remains in IR Category 5b.
