Little Sioux River IA 06-LSR-1570

The Class A1 (primary contact recreation) are assessed 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 2012 through 2014 at the Little Sioux River near Larrabee were as follows: the 2012 geometric mean was 54 orgs/100 ml, the 2013 geometric mean was 420 orgs/100 ml, and the 2014 geometric mean was 143 orgs/100 ml.  Two of the three recreation season geometric means exceeded the Class A1 geometric mean criterion of 126 orgs/100 ml.  Eight of the combined 24 samples (33%) 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 IDNR’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"

The Class B(WW1) aquatic life uses remain assessed (monitored) as “fully supported.”  Monitoring at the IDNR/SHL station near Larrabee showed no violations of Class B(WW1) water quality criteria for 36 Ammonia samples (maximum = 1.4 mg/L), 36 Dissolved Oxygen samples (minimum = 7.3 mg/L), 36 Temperature samples (maximum = 27.8° c), 36 Chloride samples (maximum = 48 mg/L), or 36 Sulfate samples (maximum = 180 mg/L) occurred during monitoring from January 2012 to December 2014.  One of the 36 samples (3%) analyzed for pH (range = 7.3 to 9.8) violated the Class B(WW1) criteria during the 2012-2014 monitoring period. According to U.S. EPA guidelines (U.S. EPA 1997b, page 3-17), a violation frequency of greater than 10% for conventional parameters such as Ammonia, Dissolved Oxygen, Temperature, Chloride, or Sulfate suggests impairment of aquatic life uses.  Because the frequency of violations for this parameters is not greater than 10 percent, these results do not suggest impairment of the Class B(WW1) aquatic life uses.

Supporting the chemical/physical water quality results and assessment, the results of the 2005 and 2012-2014 biological sampling also indicate "full support" (evaluated) of the Class B(WW1) aquatic life uses.   This evaluated biological assessment was based on data collected in 2005 and 2012-2014 as part of the IDNR/SHL REMAP and large river projects.   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 2005 FIBI score was 51 (good) and the 2005 BMIBI score was 56 (good).   The 2012 BMIBI score was 52 (fair).   The 2013 BMIBI scores were 55 (fair) and 60 (good).  The 2014 BMIBI score was 48 (fair).  The aquatic life use support was assessed (evaluated) as fully supporting (=FS), 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.   This assessment is considered evaluated because the drainage areas (1833 and 1848 mi2) above the sampling sites were greater than the maximum limit (500 mi2) that was used to calibrate the Iowa wadeable stream impairment criteria.   Even though this site passed both the FIBI (1/1) and BMIBI BICs (3/5), it is uncertain as to whether or not this segment is meeting the aquatic life criteria because the sites used for the assessment don’t fall in the calibrated watershed size.

Fish consumption uses remain "not assessed due to the lack of recent fish contaminant monitoring in this river reach.