The Class A1 (primary contact recreation) uses are assessed (monitored) 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 24 samples collected during the recreational seasons of 2014 through 2016 at DNR station 10910001 (Middle River near Indianola) were as follows: the 2014 geometric mean was 1646 orgs/100 ml, the 2015 geometric mean was 719 orgs/100 ml, and the 2016 geometric mean was 842 orgs/100 ml. All three recreation season geometric means exceeded the Class A1 geometric mean criterion of 126 orgs/100 ml. Eighteen of the combined 24 samples (75%) 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."

The Class B(WW1) aquatic life uses are assessed (evaluated) as “partially supported” based on results of DNR/SHL biological sampling in 2002 and 2012-2014 conducted as part of the REMAP and large river sampling projects. 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 2002 FIBI scores were 21 (poor) and 38 (fair). The 2012-2014 BMIBI scores were 35, 36 (both fair) and 61 (good). The aquatic life use support was assessed as partially supporting (=PS), 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 36 and the BMIBI BIC for this ecoregion is 51. This segment passed the FIBI BIC 1/2 times in 2002 and passed the BMIBI BIC 1/3 times in the last five years. This assessment is considered evaluated because the drainage area (502 mi2) above this sampling site was greater than the maximum limit (500 mi2) that was used to calibrate the Iowa wadeable stream impairment criteria. Even though this site failed both the FIBI (1/2) and BMIBI (1/3) BICs, it is uncertain as to whether or not this segment is meeting the aquatic life criteria because it doesn’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). Despite this change in assessment methodology and type, this waterbody remains in IR Category 5b-t and remains on Iowa’s Section 303(d) list of impaired waters.

Previous assessments of this stream segment have indicated potential impacts due to alteration of aquatic habitats. Thus, problems with habitat quality may explain the relatively poor IBI values for fish and aquatic macroinvertebrates.

As part of the REMAP project, diurnal dissolved oxygen/temperature monitoring conducted during July, September, and October 2002 found substantial fluctuation of dissolved oxygen levels and temperature, including nighttime sags in dissolved oxygen (<5 mg/L) and daytime temperatures exceeding 35 C (95 F). These conditions were associated with very high estimated levels of community respiration and primary production. Levels of BMIBI metrics that are sensitive to organic enrichment suggest a nutrient enrichment/algal growth-related water quality problem. Habitat modification has resulted in a wide and shallow stream channel subjected to high solar input. These physical factors probably contribute to excessive levels of algal growth, and extreme dissolved oxygen and temperature fluctuations. Additional sampling data are needed to evaluate the extent, causes and sources of this water quality concern.

Despite results of biological monitoring which suggest impairment, results of DNR/SHL ambient chemical/physical monitoring do not suggest an impairment.Monitoring showedno violations of Class B(WW1) water quality criteria for 35 Ammonia samples (maximum = 1.1 mg/L), 36 Temperature samples (maximum = 31° c), 36 Chloride samples (maximum = 34 mg/L), or 36 Sulfate samples (maximum = 69 mg/L) occurred during monitoring from January 2014 to December 2016.1 of the 36 samples (3%) analyzed for Dissolved Oxygen (minimum = 3.5 mg/L) and 1 of the 35 samples (3%) analyzed for pH (range = 6.1 to 8.9) violated the Class B(WW1) criteria during the 2014-2016 monitoring period. According to U.S. EPA guidelines (U.S. EPA 1997b, page 3-17) and Iowa DNR's assessment/listing methodology, a violation frequency of significantly greater than 10% for conventional parameters such as Dissolved Oxygen, or pH suggests impairment of aquatic life uses. Because the frequency of violations for these parameters are not greater than 10 percent, these results do not suggest impairment of the Class B(WW1) aquatic life uses.These results suggest that the Class B(WW1) aquatic life should be assessed as "fully supported."

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