Cedar River IA 02-CED-472

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 the DNR ambient monitoring station (10090001) upstream near Janesville were as follows: the 2014 geometric mean was 105 orgs/100 ml, the 2015 geometric mean was 45 orgs/100 ml, and the 2016 geometric mean was 137 orgs/100 ml. One of the three recreation season geometric means exceeded the Class A1 geometric mean criterion of 126 orgs/100 ml. Three of the combined 24 samples (12%) 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 contrast to the water quality aquatic life assessment, the aquatic life assessment based on biological sampling suggests the aquatic life uses remain "partially supporting". This evaluated biological assessment was based on data collected in 2007 and 2012-2014 as part of the DNR/SHL stream nutrient sampling project and on data collected in 2007 as part of sampling conducted by the DNR Fisheries Bureau. A series of biological metrics that 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 collected in the stream sampling reach. The biological metrics were combined a benthic macroinvertebrate index (BMIBI). The index rank the biological integrity of a stream sampling reach on a rising scale from 0 (minimum) to 100 (maximum). The 2007 FIBI score was 74 (excellent). The 2012-2014 BMIBI scores were 48, 52, 53, 54 (all fair) and 59, 65 (both good). The aquatic life use support was assessed (evaluated) as partially supporting (=PS), based on a comparison of the BMIBI scores with biological impairment criteria (BIC) established from a statistical analysis of biological data collected at stream ecoregion reference sites from 1994-2008. The artificial substrate BMIBI BIC for this ecoregion is 52 and the natural substrate BMIBI BIC is 70. This assessment is considered evaluated because the drainage area (1549 and 1671 mi2) above the sampling sites was greater than the maximum limit (500 mi2) that was used to calibrate the Iowa wadeable stream impairment criteria. The segment passed the 2013 and 2014 artificial substrate BMIBI BIC and failed the BMIBI BICs on the other four samples.

Even though this site passed the FIBI BIC in 2007 and failed the BMIBI BIC (2/6 times) 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 assessmentdon’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 remain not assessed due to the lack of recent fish tissue monitoring in this river segment.