Assessment Comments
Assessment remains based on results of a fish kill investigation in August 2008 and on results of IDNR fish kill follow-up monitoring in 2013.
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.com/water/standards/files/06mar_swc.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 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/EXPLANATION: The presumptive Class A1 (primary contact recreation) uses remain "not assessed" (IR 3a) due to a lack of information upon which to base an assessment. The assessment of the presumptive Class B(WW1) aquatic life uses is changed from “partially supporting” (IR 5b) due to an August 2008 fish kill to “not assessed” (IR 3a). This change is based on results of fish kill follow-up monitoring conducted by IDNR staff in July 2013. This change represents a de-listing of the biological (fish kill) impairment.
The presumptive Class B(WW-1) (aquatic life) uses were assessed (monitored) as "partially supported" (IR 5b) based on results of a fish kill investigation in August 2008. The kill occurred on August 7, 2008, and was attributed to aerial spraying of a fungicide. Approximately 14,510 fish were killed in about 7 miles of the stream. Results of water quality sampling showed a pyraclostrobin, a fungicide, concentration of 29 ppb. Literature indicates that this product is acutely toxic to aquatic life at approximately 11 ppb. The value of the fish killed was estimated to be $26,244.53. No responsible party was identified.
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. Thus, this assessment segment was placed in Category 5b of Iowa’s 2010 Integrated Report.
This stream segment’s fish community was sampled on July 25, 2013 as part of the IDNR Watershed Improvement and Water Monitoring sections’ fishkill follow up monitoring program. Sampling methods described in IDNR’s fish kill follow-up protocol (Attachment 5 of Iowa’s 2014 assessment/listing methodology) were followed. Approximately 585 feet of stream were sampled using a single pass with backpack electro fishing units. Results of this sampling show that this stream supports approximately 4,300 fish per mile compared to the Level IV ecoregion 47f average of approximately 1,590 fish per mile; 100% 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 fishkill follow-up sampling lack the scientific rigor to determine whether the designated aquatic life uses are “fully supported,” the results do indicate that the stream has recovered from 2008 fish kill event. Thus, this stream segment is being moved from impairment Category 5b of Iowa’s Integrated Report to Category 3a (designated use not assessed).
