Assessment Comments
Assessment remains based on an IDNR investigation of a fish kill near Washington, IA, in September 2002.
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 the lack of information upon which to base an assessment. The Class B(WW2) aquatic life uses remain assessed (monitored) as "partially supported" due to occurrence of a fish kill in September 2002. The cause of the kill remains “unknown.”
EXPLANATION: The fish kill occurred on September 19, 2002 downstream from the Washington, Iowa, wastewater treatment plant (WWTP). The investigation showed that the stream was covered with algae for 1-2 miles downstream from the facility. Dead fish were first observed from 0.5 to 0.75 miles downstream from the facility; the kill covered approximately 1.5 miles of this stream, and an estimated 12,500 fish were killed. No cause of the kill was identified. The Washington WWTP had been meeting all NPDES permit limits, and no odors, discharge pipes, or other potential causes were observed during the investigation. The leading hypothesis is that the die-off of the large amount of algae reduced oxygen levels in this stream such that aquatic life was affected.
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 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. Thus, because this kill was potentially related to a pollutant impact, this stream segment remains assessed (monitored) as "partially supported" and placed in IR Category 5b.
