West Fork Crooked Creek IA 03-SKU-921

Assessment Comments

Assessment remains based on (1) an IDNR investigation of a fish kill near Washington, IA, in September 2002 and (2) results of IDNR/SHL biological sampling in October 2010.

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 (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 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 the lack of information upon which to base an assessment.   The assessment of the presumptive Class B(WW1) aquatic life uses was changed for the 2012 IR cycle from “partially supporting” (IR Category 5b) due to a September 2000 fish kill to “not assessed” (IR 3a).   This change was based on results of biological sampling conducted by IDNR staff in October 2010.   This change represented a de-listing of the biological (fish kill) impairment.

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 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, are 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.  

This stream segment’s fish community was sampled by the Iowa State Hygienic Laboratory on October 29, 2010, as part of IDNR’s biological sampling program.   The data from this sampling were applied to IDNR’s fish kill follow-up protocol (Attachment 5 of Iowa’s 2012 assessment/listing methodology).   Approximately 850 feet of stream were sampled using a single pass with one towed barge electro fishing unit.   Results of this sampling show that this stream supports approximately 2,150 fish per mile compared to the Level IV ecoregion 47f average of approximately 1,600 fish per mile; 89% of the expected fish taxa for this ecoregion were sampled.   The results from this follow-up sampling and comparison of these results to ecoregion averages suggest that the fish community of this stream segment is similar to or better than non-fishkill impacted streams.   Although the results of the single 2010 biological sampling lacked the scientific rigor to determine whether the designated aquatic life uses are “fully supported,” the results did indicate that the stream had recovered from September 2000 fish kill event.   Thus, this stream segment was moved from an impairment category (Category 5b) to Category 3a (designated use not assessed).   This segment remains in IR Category 3a.