Assessment Comments
Assessment based on results of a fish kill investigation in August 2008 and 2006 biological sampling data: FIBI = 42 (fair), BMIBI = 62 (good). FIBI BIC = 32; BMIBI BIC = 62.
Basis for Assessment
[Note: Prior to the 2008 Section 305(b) cycle, this stream segment was designated only for Class B(WW) aquatic life uses, including fish consumption 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), and due to the completion of a Use Attainability Analysis, this segment is also now designated for Class A1 (primary contact recreation) uses. This segment remains designated for warmwater aquatic life use (now termed Class B(WW1) uses), and for fish consumption uses (now termed Class HH (human health/fish consumption uses).]
SUMMARY: The Class A1 (primary contact recreation) and fish consumption uses are "not assessed" due to the lack of information upon which to base an assessment. The Class B(WW1) aquatic life uses are assessed (monitored) as "partially supported" based on the results of a fish kill investigation in August 2008.
EXPLANATION: The fish kill occurred on or before August 29, 2008 and was caused by a discharge from a silage storage area. Approximately 31,244 fish were killed along a 16.1 mile stretch of the Winnebago River, starting where Silver Creek enters the Winnebago River in section 12 of Madison Township, Hancock County. The kill continued along the Winnebago River to the Fertile Dam in section 34 of Fertile Township, Worth County. The value of the fish was estimated to be $63,020.23. At the time of this assessment there is no information as to whether DNR sought or received restitution for this fish kill.
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 (2007-2009) 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 will be placed in Category 5b of Iowa’s 2010 Integrated Report.
Data collected in 2006 as part of the IDNR/UHL stream biological sampling project, however, suggested "full support" of the Class B(WW1) aquatic life uses. 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 2006 FIBI score was 42 (fair) and the BMIBI score was 62 (good). The aquatic life use support was assessed as fully supporting (=FS), based on a comparison of the FIBI and BMIBI scores with biological impairment criteria (BIC) established for previous Section 305(b) reports. The non-riffle habitat FIBI BIC for this ecoregion is 32 and the BMIBI BIC for this ecoregion is 62. The biological impairment criteria were determined from a statistical analysis of data collected at stream ecoregion reference sites from 1994-2004.
The aquatic life assessment based on the 2006 biological data is considered "evaluated" because there were not two or more samples collected from this segment in multiple years from 2004-2008. Despite this change in assessment methodology and type, this waterbody remains in IR Category 5b based on the 2008 fishkill.
Fish consumption uses remain "not assessed" due to the lack of fish contaminant monitoring in this stream segment.
