[Note: A TMDL for the bacterial impairment for streams in the Yellow River basin was prepared by Iowa DNR in 2012 and approved by U.S. EPA in 2013. Due to completion of the TMDL, the Integrated Report category for the Class A1 recreational uses was changed from 5a (impaired; TMDL needed) to 4a (impaired; TMDL approved).]

The Class A1 (primary contact recreation) uses are assessed (monitored) as "partially supported" based on levels of indicator bacteria that exceeded state water quality criteria. The geometric means of indicator bacteria (E. coli) in the 24 samples collected during the recreational seasons of 2014 through 2016 at DNR-SHL station 10030002 near Volney were as follows: the 2014 geometric mean was 188 orgs/100 ml, the 2015 geometric mean was 87 orgs/100 ml, and the 2016 geometric mean was 496 orgs/100 ml. Two of the three recreation season geometric means exceeded the Class A1 geometric mean criterion of 126 orgs/100 ml. Ten of the combined 24 samples (42%) exceeded Iowa’s Class A1 single-sample maximum criterion of 235 orgs/100 ml. According to U.S. EPA guidelines for Section 305(b) reporting and Iowa DNR’s assessment/listing methodology, if the geometric mean is greater than 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). Thus, because at least one recreation season geometric mean exceeded criteria for Class A1 uses, these uses are assessed as "partially supported."

In addition to chemical/physical monitoring, the assessment of aquatic life uses was also based on biological data collected in 2012 and 2015 as part of the DNR/SHL stream biocriteria 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 that were 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 2015 FIBI score was 59 (good) and the BMIBI score was 64 (good). The 2012 FIBI score was 68 (good) and the BMIBI score was 81 (excellent). 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 biological impairment criteria were determined from a statistical analysis of data collected at stream ecoregion reference sites from 1994-2008. The FIBI BIC for this ecoregion is 52 and the BMIBI BIC for this ecoregion is 61. This segment passed the FIBI and BMIBI BICs 2/2 times in the last five years (2012-2016).

This aquatic life assessment is now considered "monitored" based on a change in the 2010 DNR assessment methodology. DNR now requires a segment have two or more biological samples collected from the segment in multiple years over a recent five-year period to be considered “monitored”. This segment had multiple samples collected in the previous five years (2012-2016).

The fish consumption uses remain “not assessed” due to the lack of fish contaminant monitoring in this river reach.