French Creek IA 01-UIA-248

The presumptive Class A1 (primary contact recreation) uses and the presumptive Class A2 (secondary contact recreation) uses remain both assessed as "not supported" based on levels of indicator bacteria that exceeded state water quality criteria. The geometric mean of indicator bacteria (E. coli) in the 21 samples collected during the recreational seasons of 2012 through 2014 at Upper Iowa River station 29 were as follows: the 2012 geometric mean was 903 orgs/100 ml, the 2013 geometric mean was 2,442 orgs/100 ml, and the 2014 geometric mean was 622 orgs/100 ml. All three geometric means exceed both the Class A1 criterion of 126 orgs/100 ml, and the geometric means from 2012 and 2013 exceed the Class A2 criterion of 630 orgs/100 ml. Eighteen of the 21 samples (86%) 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).

The Class B(CW1) aquatic life uses remain assessed as "fully supporting" based on data collected in 2013 and 2016 as part of the DNR/SHL coldwater stream sampling project. A series of biological metrics which reflect coldwater 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 that were collected in the stream sampling reach. The biological metrics were combined to make a coldwater benthic index (CBI). The index ranks the biological integrity of a coldwater stream sampling reach on a rising scale from 0 (minimum) to 100 (maximum). The 2013 CBI score was 77 and the 2016 CBI score was 73. The aquatic life use support was assessed (evaluated) as fully supporting (=FS), based on a comparison of the CBI scores with biological impairment criteria (BIC) established for the 2012 Section 305(b) report. The biological impairment criteria were determined from a statistical analysis of data collected at coldwater stream reference sites from 1994-2011. The CW BIC is 60 and this segment passed the CW BIC 2/2 times in the last five years (2012-2016).

In addition, based on an updated summary of trout reproduction in Iowa streams prepared by the DNR Fisheries Bureau in January 2019, the Class B(CW1) uses are assessed as "fully supported". According to the updated summary, French Creek is in the group of Iowa coldwater streams that supports natural reproduction of trout. Based on results of surveys by the DNR Fisheries Bureau, this stream is placed in the category of Iowa trout streams that exhibit fairly consistent natural reproduction and maintain a viable population of the listed species (Brown and Brook Trout) without any stocking (Category I).

Fish consumption uses are assessed as "fully supported" based on results of DNR fish tissue monitoring in 2015. The average level of mercury in the tissue plugs from five brown trout in 2015 was 0.05 ppm (SD=0.0).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 do not exceed any of Iowa’s consumption advisory trigger levels, thus suggesting no justification for issuance of a consumption advisory for this waterbody.