Stony Creek IA 06-LSR-1644

The Class B(WW2) aquatic life uses remain assessed (evaluated) as "partially supporting" based on biological data collected in 2005 as part of the DNR/SHL stream REMAP project. A series of biological metrics which reflect stream water quality and habitat integrity were calculated from the biological sampling data. The biological metrics are based on the numbers and types of benthic macroinvertebrate taxa and fish species collected in the stream sampling reach. The biological metrics were combined to make a fish community index of biotic integrity (FIBI) and a benthic macroinvertebrate index (BMIBI). The indexes rank the biological integrity of a stream sampling reach on a rising scale from 0 (minimum) to 100 (maximum). The 2005 FIBI score was 34 (fair) and the BMIBI score was 28 (poor). The aquatic life use support was assessed as partially supporting (=PS), based on a comparison of the FIBI and BMIBI scores with biological impairment criteria (BIC) established for previous Section 305(b) reports. The FIBI BIC for this ecoregion is 43 and the BMIBI BIC for this ecoregion is 54. The biological impairment criteria were determined from a statistical analysis of data collected at stream ecoregion reference sites from 1994-2008. This segment failed both the FIBI and BMIBI BICs in 2005.

This aquatic life assessment is considered "evaluated" because there were not two or more samples collected from this segment in multiple years during a five-year period. According to DNR’s assessment/listing methodology, impairments based on “evaluated” assessments are of lesser confidence and are thus not appropriate for Section 303(d) listing (Category 5 of the Integrated Report). Additionally, because these data are now considered too old (greater than five years) to accurately characterize current water quality conditions, the assessment category is considered “evaluated” (indicating an assessment with relatively lower confidence) as opposed to "monitored" (indicating an assessment with relatively higher confidence). DNR does, however, consider these impairments as appropriate for listing under either Category 2b or 3b of the Integrated Report (waters potentially impaired and in need of further investigation). However, despite this change in assessment methodology and type, this waterbody was previously on Iowa’s Section 303(d) list and thus remains on Iowa’s Section 303(d) list of impaired waters (IR Category 5b-t).

A fish kill on this stream reach occurred on or before September 29, 2015 and was attributed to organic waste. The kill affected 18.2 miles of Stony Creek, starting in Osceola County and extending through Dickinson County to Clay County. The kill was caused by egg washing liquid that was dumped from a tank into a corn field and flowed into Stony Creek. Approximately 163,001 fish were killed with an estimated value of $25,806.30. The party responsible for the kill was identified, and restitution was sought.

According to DNR's assessment methodology for Section 305(b) reporting, occurrence of a single pollution-caused fish kill during an assessment period indicates "partial support" of the aquatic life uses. If, however, a consent order has been issued to the party responsible for the kill and monetary restitution has been sought for the fish killed, the affected waterbody should be placed in IR Category 4d (impaired but TMDL not required). Thus, this assessment segment was placed in category 4d of Iowa’s 2016 Integrated Report based on updated information regarding restitution for this (2015) fish kill and remains there for the current IR cycle.