Winnebago River IA 02-WIN-826

The Class A1 primary contact recreation uses are assessed (monitored) as "partially supported" based on results of ambient monitoring for indicator bacteria (E. coli). The geometric means of indicator bacteria (E. coli) in the 22 samples collected during the recreational seasons of 2012 through 2014 at station 10170003 downstream from Mason City were as follows: the 2012 geometric mean was 387 orgs/100 ml, the 2013 geometric mean was 222 orgs/100 ml, and the 2014 geometric mean was 371 orgs/100 ml. All three geometric means slightly exceed the Class A1 criterion of 126 orgs/100 ml. Thirteen of the 22 samples (59%) exceeded the 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 a recreation season geometric mean exceeds the respective water quality criterion, the contact recreation uses should be assessed as “impaired” (see pgs 3-33 to 3-35 of U.S. EPA 1997b).

In contrast to the water quality aquatic life assessment, the aquatic life assessment based on biological sampling suggests the aquatic life uses are "partially supporting". This evaluated biological assessment was based on data collected in 2012-2014 as part of the DNR/SHL stream nutrient sampling project and fish sampling data collected in 2012-2015 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 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 2012-2014 BMIBI scores were 48 (fair), 56, 66, 69 70 and 72 (all good). The 2012-2015 FIBI scores were 39, 42, 44 (all fair) and 81 (excellent). The aquatic life use support was assessed (evaluated) as partially supporting (=PS), based on a comparison of the BMIBI and FIBI 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. The non-riffle habitat FIBI BIC for this ecoregion is 44. This assessment is considered evaluated because the drainage area (654 and 695 mi2) above the two sampling sites was greater than the maximum limit (500 mi2) that was used to calibrate the Iowa wadeable stream impairment criteria. This segment passed the FIBI BIC 2/4 times in the last five years. This segment passed the appropriate BMIBI BICs 3/6 times in the last five years. Even though this site failed both the FIBI and BMIBI BICs, 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 remain assessed as "fully supported" based on results of U.S. EPA/DNR fish tissue (RAFT) monitoring east of Mason City in 2012 and DNR fish tissue monitoring conducted in 2015. The 2012 composite sample of fillets from common carp had low levels of contaminants: mercury: 0.122 ppm; total PCBs: <0.09 ppm; and technical chlordane: <0.03 ppm. The average level of mercury in the 2012 tissue plugs from five walleye was 0.218 ppm (SD=0.082); this level is below the one-meal-per-week advisory threshold of 0.3 ppm. The average level of mercury in the 2015 tissue plugs from five walleye was 0.092 ppm (SD=0.041); this level is also below the one-meal-per-week advisory threshold of 0.3 ppm.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 east of Mason City in 2012 and 2015 do not exceed any of Iowa’s advisory trigger levels, thus suggesting no justification for issuance of a consumption advisory for this waterbody.