Little Sioux River IA 06-LSR-1573

The Class A1 (primary contact recreation) are assessed as "not supported" based on levels of indicator bacteria that exceeded state water quality criteria. The geometric means of indicator bacteria (E. coli) in the 22 samples collected during the recreational seasons of 2012 through 2014 at the Little Sioux River downstream of Spencer were as follows: the 2012 geometric mean was 1181 orgs/100 ml, the 2013 geometric mean was 1805 orgs/100 ml, and the 2014 geometric mean was 895 orgs/100 ml. All three recreation season geometric means exceeded the Class A1 geometric mean criterion of 126 orgs/100 ml. Nineteen of the combined 22 samples (86%) 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 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 "not supported".

Regarding support of the Class B(WW1) aquatic life uses, monitoring at the DNR/SHL city station downstream from Spencer showed no violations of Class B(WW1) water quality criteria for 32 Ammonia samples (maximum = 1.3 mg/L), 33 Dissolved Oxygen samples (minimum = 7.2 mg/L), 32 pH samples (range = 7.4 to 8.7), 33 Temperature samples (maximum = 27.3 °C), 33 Chloride samples (maximum = 57 mg/L), or 33 Sulfate samples (maximum = 180 mg/L) occurred during monitoring from January 2012 to September 2014. According to U.S.EPA guidelines for Section 305(b) water quality assessments (U.S.EPA 1997b, page 3-17), the EPA guidelines allow up to 10% violations of these conventional parameters before impairment of water quality is indicated. Thus, these results thus suggest “full support” of the Class B(WW1) aquatic life uses.

However, the results from the 2005 and 2012-2014 DNR/SHL REMAP and large river biological sampling indicate the Class B(WW1) aquatic life uses should be assessed (evaluated) as "partially supported." This evaluated biological assessment was based on data collected in 2005 and 2012-2014 as part of the DNR/SHL REMAP and large river sampling 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 33 (fair). The 2012 BMIBI score was 54 (fair), the 2013 BMIBI score was 44 (fair) and the 2014 BMIBI score was 38 (fair). 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. This assessment is considered evaluated because the drainage areas (1104 and 1109 mi2) above the sampling sites were greater than the maximum limit (500 mi2) that was used to calibrate the Iowa wadeable stream impairment criteria. In addition to the large drainage area, the conditions at the time of sampling were not conducive to collecting a good fish sample. Sampling staff indicated the fish sample quality was only "fair" with excessive turbidity and width contributing to the poorer sampling conditions. Even though this site failed to meet the FIBI BIC (0/1) in 2005 and failed the BMIBI BIC (1/3) in the last five years, 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. According to DNR’s assessment/listing methodology, impairments based on “evaluated” assessments are of lesser confidence and are thus not appropriate for Section 303(d) listing (Category 5 of the Integrated Report). DNR does, however, consider these impairments as appropriate for listing under either Category 2b or 3b of the Integrated Report (waters potentially impaired and in need of further investigation).

Fish consumption uses are assessed as "fully supported" based on results of DNR fish tissue monitoring at Gillet Grove in 2011 and 2015. The 2011 composite sample of fillets from channel catfish had low levels of contaminants:mercury:0.115 ppm; total PCBs: <0.09 ppm; and technical chlordane: <0.03 ppm. The average level of mercury in the tissue plugs from five largemouth bass in 2011 was 0.289 ppm (SD=0.159). The average level of mercury in the tissue plugs from five walleye in 2015 was 0.174 ppm (SD=0.054).The existence of, or potential for, a fish consumption advisory is the basis for Section 305(b) assessments of the degree to which Iowa’s lakes and rivers support their fish consumption uses. The levels of contaminants in the tissue samples from fish collected at Gillet Grove do not exceed any of Iowa’s consumption advisory trigger levels, thus suggesting no justification for issuance of a consumption advisory for this waterbody.