Willow Creek IA 06-LSR-1626

The presumptive Class A1 (primary contact recreation) are assessed as "not supported" based on levels of indicator bacteria that exceeded state water quality criteria.   The geometric means of indicator bacteria (E.  coli) in the 13 samples collected during the recreational seasons of 2009 and 2010 at Willow Creek near Royal were as follows:  the 2009 geometric mean was 140 orgs/100 ml and the 2010 geometric mean was 1,113 orgs/100 ml.   Both geometric means exceed the Class A1 criterion of 126 orgs/100 ml.   Nine of the 13 samples (69%) 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 are "not supported" (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 “impaired.”  

The Class B(WW-2) aquatic life uses are assessed (monitored) as "partially supported" based on results of fish kill investigations in 2001, 2002 and 2006.   The most recent of these fish kills occurred on August 1, 2006 and was attributed to animal waste.   Multiple fish kills occurred in this area after heavy rains.   Very low dissolved oxygen levels, high ammonia levels (15 ppm), and the odor of manure were noted during the investigation.   Approximately 21,834 fish including bullheads, chubs, and minnows were killed within a five mile stretch of this stream near Royal.   The estimated value of these fish was $4777.06.   At the time of this assessment there are no records that IDNR has sought/received restitution for this fish kill.

A fish kill also occurred on this stream segment south of Royal on September 19, 2001.    The kill was caused by the discharge of cattle manure from an open feedlot; an estimated 8,900 fish were killed.    No estimate of the length of stream affected is available.    Water quality monitoring  conducted with a field kit during the fish kill investigation showed a dissolved oxygen concentration of zero and an ammonia-nitrogen concentration of 12.5 mg/l.  

An additional fish kill occurred on this segment on September 18, 2002.   The kill was caused by discharge of cattle manure from an open feedlot.  (NOTE: this is the same feedlot responsible for the September 2001 fish kill.)  Approximately 8988 fish were killed in a 4.3 mile stretch of stream.   The estimated value of these fish was $2093.01.

According to IDNR’s assessment/listing methodology, the occurrence of a single pollutant-caused fish kill, or a fish kill of unknown origin, on a waterbody or waterbody reach during the most recent assessment period (2008-2011) indicates a severe stress to the aquatic community and suggests that the aquatic life uses should be assessed as “impaired.”  If a cause of the kill is identified, and the cause is either known, or suspected, to be a “pollutant”, the assessment type is considered “monitored” and the affected waterbody is a candidate for Section 303(d) listing.    Fish kills attributed to a pollutant, but where a source of the pollutant was not identified and/or where enforcement actions were not taken against the responsible party, will be placed into Integrated Report subcategory 5b.   The intent of placing these waterbodies into Category 5 is not to necessarily require a TMDL but to keep the impairment highlighted due to the potential for similar future kills from the unaddressed causes and/or sources.   Thus, this assessment segment will remain in Category 5b of Iowa’s Integrated Report.    

Results of biological data collected in 2009 and 2011 as part of the IDNR/SHL biocriteria project also suggest "partial support" of the aquatic life uses.   The 2009 FIBI score was 52 (fair) and the BMIBI score was 25 (poor).   The 2011 FIBI score was 54 (fair) and the BMIBI score was 51 (fair).   The aquatic life use support was assessed (evaluated) 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 43 and the BMIBI BIC for this ecoregion is 54.   This segment passed the FIBI BIC 2/2 times and passed the BMIBI BIC 0/2 times in the last six years.

This aquatic life assessment is now considered "evaluated" based on a change in the 2010 IDNR assessment methodology.   IDNR now requires a segment have two or more biological samples collected from the segment in multiple years in the recent five year period (2010-2014) to be considered “monitored”.   This segment had multiple samples collected in the previous six years (2009-2014).  However, despite this change in assessment methodology and type, this waterbody remains in IR Category 5b but moves from sub-category 5b-v (verified) to sub-category 5b-t (tentative) and remains on Iowa’s 2016 Section 303(d) list of impaired waters.   

Results of water chemistry monitoring in 2010 and 2011, however, suggest "full support" of the Class B(WW-2) uses.   Results of chemical/physical monitoring at the station near Royal showed no violations of Class B(WW1) water quality criteria during the 2010-2011 assessment period for dissolved oxygen (minimum value = 5.9 mg/l), ammonia nitrogen (maximum value = 0.46 mg/l), temperature (maxiumum = 26.3C), or pH (range = 7.4 to 8.5 units) in the 19 samples collected.  No violations of Class B(WW1) criteria for chloride or sulfate occurred in the 12 samples collected during the 2010-11 period.   Regardless of the relatively good water chemical/physical water quality conditions suggested by the results of water quality monitoring, the results of biological sampling and the occurrence of fish kills in this assessment segment suggest that the aquatic life uses should be assessed as "impaired".

The results of continuous monitoring for dissolved oxygen (DO) and temperature in 2011 also suggest "full support" of the Class B(WW-2) uses. The lowest DO concentration recorded in 34 days of continuous monitoring was 4.9 mg/L. The daily DO minimum concentration failed to meet the 24-hour DO criterion (4 mg/L) and the 16-hour DO criterion (5 mg/L) in 0 of 34 days each. The percentages exceeding the 24-hour and 16-hour DO criteria (0.0% each) were less than (passing) the 10% impairment threshold used to assess conventional water quality parameters. The associated statistical analysis confidence level was high (>90%). The maximum stream temperature recorded during the sensor deployment period was 31.6 degrees (C). The temperature criterion for warmwater interior streams (32 C) was exceeded in 0 of 34 days. The percentage exceeding (0%) was less than (passing) the 10% impairment threshold with high statistical confidence (>90%). Based on these data, the B(WW1) aquatic life use is assessed as not impaired due to DO and temperature. The assessment type is “evaluated” because it is based on data collected from a single year within the current data assessment period. In order to meet the requirements for a “monitored” assessment, the IDNR’s continuous monitoring assessment methodology requires monitoring data from two or more years within the assessment period.