Assessment Comments
Assessment is based on results of a fish kill investigation in November 2007.
Basis for Assessment
[Note: Prior to the current (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 (see http://www.iowadnr.com/water/standards/files/06mar_swc.pdf), this segment is now presumptively 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 (2008) 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 are "not assessed" due to a lack of water quality information upon which to base an assessment. The Class B(WW-2) aquatic life uses are assessed (monitored) as "partially supported" based on results of an IDNR fish kill investigation in 2007.
EXPLANATION: The kill occurred on or before November 2, 2007 and was attributed to Zyglo, a green dye that was discharged by a local industry and passed through the Creston Wastewater Treatment Plant. Approximately 2583 fish were killed in a 4.5 mile stretch of the river near Creston. The estimated value of the fish was $ 5924.2. At the time of this assessment there are no records that IDNR has sought/received restitution for this fish kill. Because this discharge occurred through a facility with a discharge permit this assessment will be placed in Category 5a for the 2008 assessment/listing cycle.
According to IDNR’s 2008 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 (2005-2007) 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 authorized discharges (i.e., a wastewater discharge meeting permit limits) are considered for Section 303(d) listing (IR subcategory 5a) as the existing, required pollution control measures are not adequate to address this impairment, and a TMDL is needed. Thus, this assessment segment will be placed in Category 5a of Iowa’s 2008 Integrated Report.
