Winnebago River IA 02-WIN-826

[Note:  Prior to the 2008 Section 305(b) cycle, this river segment was designated only for Class B(WW) aquatic life uses, including fish consumption uses.  Due to changes in Iowa’s surface water classification that were approved by U.S. EPA in February 2008, and due to results of a Use Attainability Analysis, this segment is also now designated for Class A1 (primary contact recreation) uses.  This segment remains designated for warmwater aquatic life use (now termed Class B(WW1) uses), and for fish consumption uses (now termed Class HH (human health/fish consumption uses).]

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 IDNR’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). 

The Class B(WW1) aquatic life uses should be assessed as “fully supported” based on results of IDNR/SHL water quality monitoring downstream from Mason City (STORET station 10170003).  Monitoring at this station from January 2012 through September 2014 showed no violations of Class B(WW1) water quality criteria for dissolved oxygen, pH, ammonia-nitrogen, chloride, or sulfate in the 33 samples collected. 

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 IDNR/SHL stream nutrient sampling project and fish sampling data collected in 2012-2014 by the IDNR 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 2012-2014 FIBI scores were 39, 42 (both 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 1/3 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 IDNR’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).  IDNR 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/IDNR fish tissue (RAFT) monitoring east of Mason City in 2012.  The 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 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 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 do not exceed any of Iowa’s advisory trigger levels, thus suggesting no justification for issuance of a consumption advisory for this waterbody.