Fox River IA 04-FOX-995

The presumptive Class A1 primary contact recreation uses remain assessed (evaluated) as “partially supporting” due to violations of Iowa’s criteria for indicator bacteria (E. coli) during the 2009 recreation season. The geometric means of indicator bacteria (E. coli) in the eight samples collected during the recreational season of 2009 at each of the four USGS stations ranged from 202 to 336 orgs/100 ml. The 2009 geometric means at all four station very slightly exceeded the Class A1 criterion of 126 orgs/100 ml. From one to three samples at each station (from 12 to 38%) 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). Thus, because at the 2009 recreation season geometric means at these USGS stations exceeded criteria for Class A1 uses, these uses are assessed as “partially supported”.

The Class B(WW2) aquatic life uses are assessed (monitored) as “partially supported" based on biological data collected in 2010 and 2013 as part of the DNR/SHL stream 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 2010 FIBI scores were 24 (poor) and 30 (fair). The 2010 BMIBI scores were 49 and 55 (both fair). The 2013 FIBI score was 20 (poor) and the BMIBI score was 16 (poor). 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 33 and the BMIBI BIC for this ecoregion is 41. This segment passed the FIBI BIC 0/3 times and passed the BMIBI BIC 2/3 times in the last seven years.

This aquatic life assessment is considered "evaluated" based on a change in the 2010 DNR assessment methodology. DNR requires a segment have two or more biological samples collected from the segment in multiple years in a five-year period to be considered “monitored”. This segment had multiple samples collected in the last seven years (2010-2016). 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). However, despite this change in assessment methodology and type, this waterbody remains in IR Category 5b-t and remains on Iowa’s 2018 Section 303(d) list of impaired waters.

As part of the REMAP project, diurnal dissolved oxygen and temperature monitoring conducted during July 2002 found dissolved oxygen levels sagging to approximately 4.2 mg/L during night hours. Additional sampling data are needed to evaluate the extent, causes and sources of this water quality problem. Stream physical habitat assessment found excessive sediment deposits and a lack of instream cover that could also contribute to the biological impairment. The wide-shallow channel probably contributes to observed high stream temperature (>36C) and high rates of biological community respiration and primary production.

Results of chemical/physical monitoring at the four USGS stations from March to December 2009 showed no violations of Class B(WW2) water quality criteria for ammonia, dissolved oxygen, or pH in the 10 samples collected at each station. These results are somewhat in contrast to results from USGS monitoring in 1998-99 at these stations which suggested potential problems with levels of dissolved oxygen and ammonia at the West Grove station near the headwaters of the Fox River. Results from 2009 from this station, however, show no violations of criteria for either dissolved oxygen (minimum: 7.7 mg/l) or ammonia (maximum: 0.42 mg/l) in the 10 samples collected. A comparison of ammonia levels at the West Grove and Paris stations in the 1998-99 versus 2009 time periods suggest significant declines in levels of ammonia in this segment of the Fox River. While average ammonia levels at the West Grove state approached 1 mg/l in the 1998-99 period, levels in the samples collected at this station in 2009 tend to be at or near the level of detection (0.02 mg/l). A complicating factor in this comparison that unfiltered water samples were analyzed for ammonia in 1998-99 (USGS parameter code 610) while filtered samples were analyzed during 2009 (USGS parameter code 608).

For more information on previous assessments for this river segment, see the assessment for the 2010 assessment/listing cycle.