Winnebago River IA 02-WIN-830

The Class B(WW1) aquatic life uses remainassessed (evaluated) as "partially supported" based on the results of a fish kill that 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. Updated information shows that DNR sought and received restitution from this fish kill.

According to DNR’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. 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 will be placed in IR Category 4d (impaired but TMDL not required). DNR feels that (1) TMDLs should not be required for kills caused by a one-time illegal or unauthorized release of manure or other toxic substance where enforcement actions were taken and (2) enforcement action is more appropriate, efficient, and effective for addressing a spill-related impairment than is the TMDL process. Thus, this assessment segment remained in Category 4d of Iowa’s 2010-2014 Integrated Reports. According to Iowa DNR’s assessment/listing methodology, if no additional fish kills have occurred over at least a five-year period, the assessment of impairment should be considered “evaluated” (i.e., of lower confidence), and the waterbody segment should be moved from IR Category 4d to IR Category 3b (list of waters in need of further investigation). This, this assessment was moved from IR Category 4d (impaired; TMDL not required) to IR Category 3b (potentially impaired) in the 2016 IR cycle.

Data collected in 2006 (prior to the fish kill in 2008) as part of the DNR/SHL 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 1994-2008.

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 2012-2016. Also, 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).

Fish consumption uses remain "not assessed" due to the lack of fish contaminant monitoring in this stream segment.