Little Rock River IA 06-BSR-1798

The Class A1 uses remain assessed (evaluated) as "not supported" based on results of ambient monitoring for indicator bacteria (E.coli). The geometric mean level of indicator bacteria (E.coli) in the 18 samples collected at the DNR/SHL TMDL monitoring station near Doon during summer recreational seasons of 2002-2003 (311 orgs/100ml) exceeds the Iowa Class A1 water quality criterion of 126 orgs/100ml. Ten of the 18 samples (56%) exceed Iowa’s single-sample maximum criterion of 235 orgs/100 ml. According to U.S. EPA guidelines for Section 305(b) reporting and according to DNR’s assessment/listing methodology, if the geometric mean level of E.coli is greater than the state criterion of 126 orgs/100 ml., the primary contact recreation uses should be assessed as "impaired" (see pgs 3-33 to 3-35 of U.S.EPA 1997b).

For the 2016 IR cycle, the assessment of the Class B(WW2) aquatic life uses was changed from "partially supported" (IR 5b) to "not assessed" (IR 3a) based on results of a fish kill follow-up survey in September 2015. A fish kill occurred in this stream segment on or before September 3, 2013. A total of 522 fish were killed over 1.75 miles of stream. The value of the fish was reported as $2,349.35. The cause of the kill was identified as a spill of animal waste from an open cattle feedlot. The following is from the fish kill investigation report:

"Runoff from two open feedlots. Dead fish were observed downstream of the confluence of two small drainage ways on the Little Rock River. DNR enumerated all dead fish – there are no expansions.This was possible because the event did not impact large numbers of small fish (minnows/shiners) and the kill extended 1.75 miles."

This stream segment’s fish community was sampled on September 3, 2015, as part of the DNR Watershed Improvement and Water Monitoring sections’ fish kill follow up monitoring program. Sampling methods described in DNR’s fish kill follow-up protocol (Attachment 5 of Iowa’s assessment/listing methodology) were followed. Approximately 985 feet of stream were sampled using a single pass with two backpack electro fishing units. Results of this sampling show that this stream supports approximately 5,640 fish per mile compared to the Level IV ecoregion 47a average of approximately 525 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 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 the September 2013 fish kill event. Thus, the assessment of aquatic life use support for this stream segment was moved from impairment Category 5b of Iowa’s Integrated Report to Category 3a (designated use not assessed).