Unnamed Tributary to Little Sioux River IA 06-LSR-6342

The presumptive Class B(WW-1) (aquatic life) uses are assessed (monitored) as "partially supported" due to the occurrence of a fish kill in September 2011. The kill occurred about 3 miles NE of Peterson just north of the Bertram Wildlife Area on or before September 19, 2011; approximately 24 fish were killed over two miles of stream.There were no valuations developed for either the value of the fish killed or the cost of the DNR investigation. The cause of the kill was identified as swine manure from a 4,000-head confinement. According to the DNR fish kill report, a water line broke as the operator was trying to lower the level in pits by pumping to a field. The DNR Fisheries Bureau did not investigate; thus, no estimates were developed for the number of fish. DNR ESD staff listed the number of fish killed as "a few dozen".

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.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.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). At the time of this assessment, there is no indication that DNR has sought or received restitution for this fish kill. Thus, this assessment segment was placed in Category 5b of Iowa’s 2014 Integrated Report and remains in that category.

Results of biological monitoring also suggest "partial support" of the presumptive Class B(WW1) aquatic life uses. This evaluated biological assessment was based on data collected from 2013 to 2014 as part of the DNR/SHL headwater stream sampling project. A series of biological metrics that reflect stream water quality and habitat integrity were calculated from the biocriteria 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 FIBI scores (n=3) ranged from 13 (poor) to 27 (fair) and the BMIBI scores (n=5) ranged from 26 (poor) to 69 (good). The aquatic life use support was assessed (evaluated) as partially supporting (=PS), based on a comparison of the FIBI and BMIBI scores with biological impairment criteria (BIC) established from a statistical analysis of data collected at stream ecoregion reference sites from 1994-2008. The FIBI BIC for this ecoregion is 43 and the BMIBI BIC for this ecoregion is 54.Even though this site passed the FIBI BIC 0/3 and BMIBI BICs 1/5 times, it is uncertain as to whether or not this segment is meeting the aquatic life criteria because it is a small headwater stream and doesn’t fall in the calibrated watershed size.

This biological assessment is considered “evaluated” (of lower confidence) due to the lack of a biological assessment protocol for headwater streams. Prior to the changes in Iowa’s surface water classification that were approved by U.S. EPA in February 2008, this stream was classified only for general uses due to the inability of the stream to support a viable aquatic community at low-flow conditions. DNR’s existing biological assessment protocol, however, was calibrated to aquatic life reference conditions in larger wadeable streams with perennial flow. The aquatic environment of most headwater streams is one of extremes in water quality.Consequently, intermittent headwater streams tend to have biological diversity that is low relative to more stable aquatic environments of larger streams with perennial flow. Thus, the use of biological assessment methods developed for the ecologically more stable and diverse streams will likely overstate the existence of impairment in headwater streams. For these reasons, headwater stream reaches that show a failure to meet regional expectations for aquatic biota (fish or aquatic macroinvertebrates) will not be added to Iowa’s Section 303(d) list of impaired waters (Category 5 of the Integrated Report). The assessment type for these assessed waters will be considered "evaluated" (indicating an assessment with relatively lower confidence) as opposed to “monitored" (indicating an assessment with relatively high confidence). Such waters are typically placed in either Category 2b or 3b of the IR and are added to the state’s list of “waters in need of further investigation”.